BBA - General Subjects (v.1760, #2)
Editorial Board (ii).
Reviewer Acknowledgment (119-124).
Molecular characterization of two acetylcholinesterase genes from the oriental tobacco budworm, Helicoverpa assulta (Guenée) by Dae-Weon Lee; Sung-Su Kim; Seung Won Shin; Won Tae Kim; Kyung Saeng Boo (125-133).
Acetylcholinesterase (AChE) has been known to be the target of organophosphorous and carbamate insecticides. Only a single AChE, however, existed in insects and was involved in insecticide resistance, recently another AChE is reported in mosquitoes and aphids. We have cloned cDNAs encoding two ace genes, designated as Ha-ace1 and Ha-ace2 by a combined degenerate PCR and RACE strategy from adult heads of the oriental tobacco budworm, Helicoverpa assulta. The Ha-ace1 and Ha-ace2 genes encode 664 and 647 amino acids, respectively and have conserved motifs including a catalytic triad, a choline-binding site and an acyl pocket. Both Ha-AChEs were determined to be secretory proteins based on the existence of a signal peptide. The Ha-ace1 gene, the first reported ace1 in lepidopterans, belongs to the ace1 subfamily whereas the Ha-ace2 gene showed high similarity to those in the ace2 subfamily. Phylogenetic analysis showed that the Ha-ace1 gene was completely diverged from the Ha-ace2, suggesting that the Ha-ace genes are duplicated. Quantitative real time-PCR revealed that expression level of the Ha-ace1 gene was much higher than that of the Ha-ace2 in all body parts examined. The biochemical properties of purified proteins by affinity chromatography showed substrate specificity for acetylthiocholine iodide, and inhibitor specificity for BW284C51 and eserine and their peptide sequences partially identified by a MALDI-TOF mass spectrometer demonstrated that two Ha-AChEs were expressed in vivo.
Keywords: Helicoverpa assulta; Acetylcholinesterase; Catalytic triad; Acyl pocket; Choline-binding site; In vivo expression;
Extracellular trehalose utilization by Saccharomyces cerevisiae by Arghya Basu; Soma Bhattacharyya; Paramita Chaudhuri; Subhabrata Sengupta; Anil K. Ghosh (134-140).
Two haploid strains of Saccharomyces cerevisiae viz. MATα and MATa were grown in glucose and trehalose medium and growth patterns were compared. Both strains show similar growth, except for an extended lag phase in trehalose grown cells. In both trehalose grown strains increase in activities of both extracellular trehalase activities and simultaneous decrease in extracellular trehalose level was seen. This coincided with a sharp increase in extracellular glucose level and beginning of log phase of growth. Alcohol production was also observed. Secreted trehalase activity was detected, in addition to periplasmic activity. It appeared that extracellular trehalose was hydrolyzed into glucose by extracellular trehalase activity. This glucose was utilized by the cells for growth. The alcohol formation was due to the fermentation of glucose. Addition of extracellular trehalase caused reduction in the lag phase when grown in trehalose medium, supporting our hypothesis of extracellular utilization of trehalose.
Keywords: Trehalose utilization; Trehalose; Secreted trehalase; Alcohol production;
TFAM-dependent and independent dynamics of mtDNA levels in C2C12 myoblasts caused by redox stress by Heiko Noack; Tobias Bednarek; Juliana Heidler; Roman Ladig; Jürgen Holtz; Marten Szibor (141-150).
TFAM is an essential protein factor for the initiation of transcription of the mtDNA. It also functions as a packaging factor, which stabilizes the mtDNA pool. To investigate the regulatory role of TFAM for regeneration and proliferation of the mtDNA pool, we exposed the muscle cell line C2C12 to a severe redox stress (H2O2) or to a moderate redox stress (GSH depletion), determined the dynamics of the mtDNA levels and correlated this with the TFAM protein levels.H2O2 caused a concentration-dependent loss of mtDNA molecules. The mtDNA levels recovered slowly within 3 days after H2O2 stress. The TFAM protein was less degraded than the mtDNA indicating an accumulation of TFAM protein per mtDNA after H2O2 stress. Overexpression of TFAM did not protect against the mtDNA loss after H2O2 stress but shortened the recovery time. GSH depletion led to a proliferation of the mtDNA pool. Although the mtDNA levels increased the TFAM protein levels were unaffected by the GSH depletion.We conclude that the accumulation of the TFAM protein after H2O2 stress contributes to the regeneration of the mtDNA pool but that other mechanisms, independent from the TFAM protein amount have to be postulated to explain the proliferation of the mtDNA pool after GSH depletion.
Keywords: TFAM; mtTFA; mtDNA; Regeneration; Proliferation; Redox stress;
Radiation-induced upregulation of γ-glutamyltransferase in colon carcinoma cells is mediated through the Ras signal transduction pathway by Serhiy Pankiv; Seila Møller; Geir Bjørkøy; Ugo Moens; Nils-Erik Huseby (151-157).
The activity of γ-glutamyltransferase (GGT) is frequently upregulated in tumor cells after oxidative stress and may thus increase the availability of amino acids needed for biosynthesis of the antioxidant glutathione. As γ-radiation of tumor cells can result in oxidative stress, we investigated whether such treatments modulate the enzyme level in colon carcinoma CC531 cells. Radiation of these cells blocked cell proliferation, increased cellular size, initiated apoptosis and upregulated GGT activity and protein levels in a dose- and time-related manner. A slight but significant increase in the cellular level of reactive oxygen species (ROS) was found directly after radiation but appeared not to cause the GGT elevation. Thus, other mechanisms than cellular oxidative stress appear to be responsible for the radiation-induced upregulation of GGT. Stable transfection of activated Ras in a human colon carcinoma cell line expressing wild-type Ras resulted in an increased GGT level, while a reduced enzyme level was demonstrated in another cell line with constitutively activated Ras after stably transfection with a dominant-negative Ras mutant. Moreover, addition of specific protein kinase inhibitors that blocked downstream targets PI-3K and MEK1/2 of Ras, prior to and after radiation, attenuated the radiation-induced activation of GGT. These results support a role for Ras, being frequently activated after radiation, in regulating the level of GGT and also indicate that GGT participates in radioresistance.
Keywords: γ-glutamyltransferase; Glutathione; Oxidative stress; Radioactive irradiation; Colon carcinoma cell;
Functional expression of lepidopteran-selective neurotoxin in baculovirus: Potential for effective pest management by Wudayagiri Rajendra; Kevin J. Hackett; Ellen Buckley; Bruce D. Hammock (158-163).
Recombinant baculovirus expressing insect-selective neurotoxins derived from venomous animals are considered as an attractive alternative to chemical insecticides for efficient insect control agents. Recently we identified and characterized a novel lepidopteran-selective toxin, Buthus tamulus insect-selective toxin (ButaIT), having 37 amino acids and eight half cysteine residues from the venom of the South Indian red scorpion, Mesobuthus tamulus. The synthetic toxin gene containing the ButaIT sequence in frame to the bombyxin signal sequence was engineered into a polyhedrin positive Autographa californica nuclear polyhedrosis virus (AcMNPV) genome under the control of the p10 promoter. Toxin expression in the haemolymph of infected larvae of Heliothis virescens and also in an insect cell culture system was confirmed by western blot analysis using antibody raised against the GST-ButaIT fusion protein. The recombinant NPV (ButaIT-NPV) showed enhanced insecticidal activity on the larvae of Heliothis virescens as evidenced by a significant reduction in median survival time (ST50) and also a greater reduction in feeding damage as compared to the wild-type AcMNPV.
Keywords: Baculovirus; Lepidopteran-selective toxin; Recombinant biopesticide; Heliothis virescens; Mesobuthus tamulus; Scorpion venom; Integrated pest management;
Assessment of anti-estrogenic activity of tamoxifen in transgenic mice expressing an enhanced green fluorescent protein gene regulated by estrogen response element by Yoshihiro Hayashi; Katsumi Toda; Toshiji Saibara; Teruhiko Okada; Hideaki Enzan (164-171).
Tamoxifen is an anti-estrogenic agent for the treatment of breast cancer, while exhibiting estrogenic activity in such tissues as the uterus. This study aimed to test whether these opposite properties of tamoxifen in the uterus can be evaluated separately in vivo. We employed two transgenic murine models named, respectively, the ERE-EGFP Ar+/+ mouse and ERE-EGFP Ar−/− mouse. Both types of mice possess an enhanced green fluorescent protein (EGFP) gene regulated by four copies of estrogen response elements (EREs), while the latter lacks a functional aromatase gene, which encodes an enzyme catalyzing conversion of androgens to estrogens. Tamoxifen clearly exhibited estrogenic activity in the uteri of ERE-EGFP Ar−/− mice, as it caused uterine wet weight gain and E2-target gene induction, as 17β-estradiol (E2) did. However, tamoxifen did not enhance the EGFP expression in ERE-EGFP Ar−/− mice, although E2 induced it significantly. In ERE-EGFP Ar+/+ mice, tamoxifen suppressed the EGFP expression in a time- and dose-dependent manner. Thus, the present study demonstrated that estrogenic and anti-estrogenic activities of tamoxifen can be evaluated by using ERE-EGFP Ar−/− and ERE-EGFP Ar+/+ mice, respectively. Furthermore, these animal models are useful to select and evaluate estrogenic and anti-estrogenic activities of chemical compounds.
Keywords: Aromatase; Estrogen; EGFP; Knockout mouse; Tamoxifen;
The nitrate/nitrite ABC transporter of Phormidium laminosum: Phosphorylation state of NrtA is not involved in its substrate binding activity by Daniel Nagore; Begoña Sanz; Javier Soria; Marta Llarena; María J. Llama; Juan J. Calvete; Juan L. Serra (172-181).
Most cyanobacteria take up nitrate or nitrite through a multisubunit ABC transporter (ATP-binding cassette) located in the cytoplasmic membrane. Nitrate and nitrite transport activity is instantaneously blocked by the presence of ammonium in the medium. Previous biochemical studies reported the existence of phosphorylation/dephosphorylation events of the nitrate transporter (NRT) related to the presence of ammonium-sensitive kinase/phosphatase activities in plasma membranes of the cyanobacterium Synechococcus elongatus PCC 6301. In this work, we have analyzed the biochemical properties of the periplasmic nitrate/nitrite-binding subunit (NrtA) of NRT from the thermophilic nondiazotrophic cyanobacterium Phormidium laminosum. Our results show that cyanobacterial NrtA is phosphorylated in vivo. However, substrate binding activity in vitro is not affected by the phosphorylation state of the protein, ruling out the possibility that phosphorylation/dephosphorylation of NrtA is involved in the regulation of the nitrate/nitrite uptake by NRT transporter. Moreover, NrtA is present as multiple isoforms showing the same molecular mass but different isoelectric points ranging from pI 5 to 6. Mass spectrometric characterization of NrtA isoforms shows that the protein is phosphorylated at residue Tyr203, and contains several methionine sulphoxide residues which account for the observed isoforms. Both phosphorylated and non-phosphorylated forms of NrtA are active in vitro, showing comparable binding affinity for nitrate and nitrite. Both substrates behave as pure competitive inhibitors with a binding stoichiometry of one molecule of anion per NrtA monomer.
Keywords: NrtA; Tyrosine phosphorylation; Nitrate/nitrite transport; Nitrogen metabolism; Cyanobacteria; Phormidium laminosum;
Wound-induced expression of the ferulate 5-hydroxylase gene in Camptotheca acuminata by Young Jin Kim; Dong Gwan Kim; Sun Hi Lee; Incheol Lee (182-190).
The phenylpropanoid pathway plays important roles in plants following exposure to environmental stresses, such as wounding and pathogen attack, which lead to the production of a variety of compounds, including lignin, flavonoids and phytoalexins. Ferulate 5-hydroxylase (F5H) is a cytochrome P450-dependent monooxygenase that catalyses the hydroxylation of ferulic acid, coniferaldehyde and coniferyl alcohol, leading to sinapic acid and syringyl lignin biosynthesis. We isolated F5H cDNA and genomic DNA from Camptotheca acuminata and investigated the expression pattern of the C. acuminata F5H (CaF5H1) gene in response to wounding. A search against the BLOCKS database of conserved protein motifs indicated that CaF5H1 retains features in common with F5Hs reported from other plants. 5′-flanking region analysis using the PLACE database showed that putative regulatory elements related to various abiotic and biotic stresses, such as drought, wounding, low temperature and pathogens, exist in the 5′-flanking region of CaF5H1. Based upon these analysis results, we investigated the expression pattern of CaF5H1 gene in response to wounding and stress-related molecules. Here, we show that CaF5H1 transcripts accumulated in the leaves in response to mechanical wounding or the application of molecules involved in the stress response, such as ethylene, ABA and hydrogen peroxide (H2O2). The application of salicylic acid and diphenylene iodonium (DPI) inhibited the wound-induced expression of CaF5H1. Taken together, we suggest that wound-induced expression of CaF5H1 may be mediated by MJ and H2O2 and enhanced phenylpropanoid contents via CaF5H1 maybe function in response to various stresses, including wounding, in plants.
Keywords: Ferulate 5-hydroxylase; Lignin; Stress molecule; Wound response;
Cloning, purification and biochemical characterization of metallic-ions independent and thermoactive l-arabinose isomerase from the Bacillus stearothermophilus US100 strain by Moez Rhimi; Samir Bejar (191-199).
The araA gene encoding l-arabinose isomerase from Bacillus stearothermophilus US100 strain was cloned, sequenced and over-expressed in E. coli. This gene encodes a 496-amino acid protein with a calculated molecular weight of 56.161 kDa. Its amino acid sequence displays the highest identity with L-AI from Thermus sp. IM6501 (98%) and that of Geobacillus stearothermophilus T6 (97%). According to SDS-PAGE analysis, under reducing and non-reducing conditions, the recombinant enzyme has an apparent molecular weight of nearly 225 kDa, composed of four identical 56-kDa subunits. The L-AI US100 was optimally active at pH 7.5 and 80 °C. It was distinguishable by its behavior towards divalent ions. Indeed, the L-AI US100 activity and thermostability were totally independent for metallic ions until 65 °C. At temperatures above 65 °C, the enzyme was also independent for metallic ions for its activity but its thermostability was obviously improved in presence of only 0.2 mM Co2+ and 1 mM Mn2+. The V max values were calculated to be 41.3 U/mg for l-arabinose and 8.9 U/mg for d-galactose. Their catalytic efficiencies (k cat /K m) for l-arabinose and d-galactose were, respectively, 71.4 and 8.46 mM−1 min−1. L-AI US100 converted the d-galactose into d-tagatose with a high conversion rate of 48% after 7 h at 70 °C.
Keywords: l-arabinose isomerase; Cloning; Purification; Metallic ion demand; d-tagatose;
Kinetic analysis of the inhibition of human butyrylcholinesterase with cymserine by Mohammad A. Kamal; Abdulaziz A. Al-Jafari; Qian-Sheng Yu; Nigel H. Greig (200-206).
Accompanying the gradual rise in the average age of the population of most industrialized countries is a regrettable progressive rise in the number of individuals afflicted with age-related neurodegenerative disorders, epitomized by Alzheimer's disease (AD) but, additionally, including Parkinson's disease (PD) and stroke. The primary therapeutic strategy, to date, involves the use of cholinesterases inhibitors (ChEIs) to amplify residual cholinergic activity. The enzyme, acetylcholinesterase (AChE), along with other elements of the cholinergic system is depleted in the AD brain. In contrast, however, its sister enzyme, butyrylcholinesterase (BuChE), that likewise cleaves acetylcholine (ACh), is elevated and both AChE and BuChE co-localize in high amounts with the classical pathological hallmarks of AD. The mismatch between increased brain BuChE and depleted levels of both ACh and AChE, particularly late in the disease, has supported the design and development of new ChEIs with a preference for BuChE; exemplified by the novel agent, cymserine, whose binding kinetics are characterized for the first time. Specifically, as assessed by the Ellman method, cymserine demonstrated potent concentration-dependent binding with human BuChE. The IC50 was determined as 63 to 100 nM at the substrate concentration range of 25 to 800 μM BuSCh. In addition, the following new binding constants were investigated for human BuChE inhibition by cymserine: T FPνβ, K νβ, K Bs, K MIBA, M IC50, D Sc, R f, O K m, OIC100, K sl, θ max and R i. These new kinetic constants may open new avenues for the kinetic study of the inhibition of a broad array of other enzymes by a wide variety of inhibitors. In synopsis, cymserine proved to be a potent inhibitor of human BuChE in comparison to its structural analogue, phenserine.
Keywords: Alzheimer's disease; Butyrylcholinestrase; Cymserine; Enzyme inhibition kinetics; New kinetic constant; Phenserine;
Increased blood plasma hydrolysis of acetylsalicylic acid in type 2 diabetic patients: A role of plasma esterases by Peter Grešner; Martin Dolník; Iveta Waczulíková; Maria Bryszewska; Libuša Šikurová; Cezary Watala (207-215).
Hydrolysis of acetylsalicylic acid (ASA, aspirin), an antiplatelet drug commonly used in the prevention of stroke and myocardial infarction, seems to play a crucial role in its pharmacological action. Thirty-eight healthy volunteers and 38 type 2 diabetic patients were enrolled to test the hypothesis that the enhanced plasma degradation and lowered bioavailability of ASA in diabetic patients is associated with the attenuation of platelet response. Aspirin esterase activities were tested at pH 7.4 and 5.5. A significantly higher overall aspirin esterase activity was noted at pH 7.4 in the diabetic patients (P < 0.003), corresponding to faster ASA hydrolysis (P < 0.006). This increased activity was attributable to butyrylcholinesterase and probably to albumin, because it was effectively inhibited by eserine and 4-bis-nitrophenyl phosphate (P < 0.01). No significant differences between control and diabetic subjects were found at pH 5.5 in either enzymatic activities or ASA hydrolysis rates. The enhanced plasma ASA degradation in diabetic subjects was significantly associated with the refractoriness of blood platelets to ASA (P < 0.05) and modulated by plasma cholesterol (P < 0.01). No direct effects of plasma pH or albumin were observed. In conclusion, higher aspirin esterase activity contributes to the lowered response of diabetic platelets to ASA-mediated antiplatelet therapy.
Keywords: Aspirin; Aspirin hydrolysis; Aspirin esterases; Butyrylcholinesterase; Aspirin resistance; Blood platelets;
Enzymatic oxidation of dipyridamole in homogeneous and micellar solutions in the horseradish peroxidase–hydrogen peroxide system by Luis Eduardo Almeida; Hidetake Imasato; Marcel Tabak (216-226).
Enzymatic oxidation of dipyridamole (DIP) by horseradish peroxidase–hydrogen peroxide system (HRP–H2O2) in aqueous and micellar solutions was carried out. The reaction was monitored by optical absorption and fluorescence techniques. In aqueous solution at pH 7.0 and pH 9.0, the disappearance of the characteristic bands of DIP centered at 400 nm and 280 nm was observed. A new strong band at 260 nm is observed for the oxidation product (s) with shoulders at 322 nm and 390 nm. A non-fluorescent product is formed upon oxidation. In cationic cethyl trimethyl-1-ammonium chloride (CTAC) and zwitterionic 3-(N-hexadecyl-N,N-dimethylammonium) propane sulfonate (HPS) micellar solutions the same results are observed: three, well-defined, isosbestic points in the optical spectra suggest the transformation between two species. In anionic micellar sodium dodecylsulfate solution (SDS), the appearance of a new band centered around 506 nm was observed, associated to a solution color change from the usual yellow to deep blue/violet, characteristic of a radical species associated to the one-electron oxidation of DIP to its cation radical (DIP·+), observed previously in electrochemical oxidation. Experiments of radical decay kinetics monitoring the absorbance change at 506 nm were performed and analyzed in the frame of a kinetic model taking into account the species both in homogeneous and micellar media. The reaction medium is composed of bulk solution, SDS micelle/solution interface and enzyme catalytic site (s). The variation of DIP·+ concentration was analyzed assuming: (1) synthesis of DIP·+ by HRP through one-electron oxidation; (2) decomposition of DIP·+ by further one-electron oxidation; (3) direct two-electron oxidation of DIP by HRP; (4) bimolecular DIP·+ disproportionation. The main results of the analysis are as follows: (1) kinetic data can be divided in two phases, an HRP active phase and another phase which proceeds in the absence of enzyme activity due to consumption of all H2O2; (2) the reactions of DIP·+ formation, DIP·+ decomposition and DIP two-electron oxidation are HRP concentration dependent; (3) since DIP·+ formation constant seems to be overestimated, it is proposed that two-electron oxidation is another source of DIP·+, through the comproportionation reaction. Evidences for this reaction were also observed previously in electrochemical experiments; and (4) the kinetic analysis provides evidences that the bimolecular reaction of DIP·+ takes place mainly in the absence of active HRP and in this phase the combination of, at least, two second-order kinetic processes is needed to model the experimental data. Our data suggest that HRP oxidizes DIP in general by a two-electron process or that the cation radical is very unstable so that the one-electron process is only detected in the presence of anionic surfactant, which stabilizes significantly the DIP·+ intermediate.
Keywords: Enzymatic oxidation; Dipyridamole; UV-VIS spectroscopy; Radical cation; Surfactant;
PLGA-microsphere mediated clearance of bilirubin in temporarily hyperbilirubinemic rats: An alternate strategy for the treatment of experimental jaundice by N. Ahmad; K. Arif; S.M. Faisal; M.K. Neyaz; S. Tayyab; M. Owais (227-232).
In the present study, we have demonstrated the suitability of microspheres in removal of plasma bilirubin from systemic circulation of hyperbilirubinemic rats. Poly (lactide co-glycolide) microspheres (PLGA microspheres) have been shown to bind with bilirubin in both a concentration and time dependent manner. The binding affinity of bilirubin to microspheres was enhanced when rat serum albumin (RSA) was loaded into the microspheres. On evaluating the potential of microspheres in elimination of bilirubin from the systemic circulation, RSA bearing microspheres were found to be competent in both removing bilirubin from the systemic circulation and controlling elevated plasma levels of liver function enzymes in temporarily hyperbilirubinemic rats. On the basis of results of the present study, we suggest that microsphere-based delivery system may help in development of safe, effective and alternate strategy for the treatment of hyperbilirubinemic conditions in model animals.
Keywords: Microsphere; Bilirubin; Serum albumin; Hyperbilirubinemia; Jaundice;
Mechanisms of γ-glutamylcysteine ligase regulation by Dikran Toroser; Connie S. Yarian; William C. Orr; Rajindar S. Sohal (233-244).
The principal objective of this study was to investigate the mechanisms regulating the activity of γ-glutamylcysteine ligase (GCL; EC 220.127.116.11), the rate limiting enzyme in glutathione biosynthesis. Two phylogenetically divergent species, mouse and the fruitfly, Drosophila melanogaster were used to test the hypothesis that reversible protein phosphorylation and pyridine dinucleotide phosphate dependent allostery regulate GCL activity. GCL was almost completely inhibited under phosphorylating conditions, involving preincubations with MgATP and endogenous protein kinases. Maximal GCL inhibitions of 94%, 77%, 85%, 87%, 83%, 95% and 89% occurred, respectively, in mouse cerebellum, hippocampus, brainstem, striatum, cortex and heart, and Drosophila. These changes in GCL activity were detected using saturating levels of substrates, suggesting that V max was dramatically affected, whereas K m values showed no differences. In vitro activation of GCL, presumably due to dephosphorylation, was blocked by inhibitors of protein phosphatases, suggesting that GCL exists in vivo as a mixture of phosphorylated and dephosphorylated forms. The reversibility of the dephosphorylation-dependent activation was indicated by the time-dependent inactivation of the in vitro activated Drosophila GCL, by preincubation with MgATP. NADPH increased maximal GCL activity by up to 93%, whereas several other nucleotide analogues did not, thereby demonstrating specificity. Kinetic analysis using Hanes–Woolf replots of initial velocity data suggested that the NADPH-dependent stimulation of GCL activity is brought about by a change in the maximal activity, V max, rather than changes in substrate affinity. Results of this study suggest that mechanisms of modulation of eukaryotic GCL enzymes may include specific binding of ligands such as pyridine dinucleotide phosphates and reversible protein phosphorylation.
Keywords: γ-glutamylcysteine ligase; Signal transduction; Phosphorylation; Glutathione; Oxidative stress;
Purification and characterisation of a novel enantioselective epoxide hydrolase from Aspergillus niger M200 by Michael Kotik; Pavel Kyslík (245-252).
Purification of a novel enantioselective epoxide hydrolase from Aspergillus niger M200 has been achieved using ammonium sulphate precipitation, ionic exchange, hydrophobic interaction, and size-exclusion chromatography, in conjunction with two additional chromatographic steps employing hydroxylapatite, and Mimetic Green. The enzyme was purified 186-fold with a yield of 15%. The apparent molecular mass of the enzyme was determined to be 77 kDa under native conditions and 40 kDa under denaturing conditions, implying a dimeric structure of the native enzyme. The isoelectric point of the enzyme was estimated to be 4.0 by isoelectric focusing electrophoresis. The enzyme has a broad substrate specificity with highest specificities towards tert-butyl glycidyl ether, para-nitrostyrene oxide, benzyl glycidyl ether, and styrene oxide. Enantiomeric ratios of 30 to more than 100 were determined for the hydrolysis reactions of 4 epoxidic substrates using the purified enzyme at a reaction temperature of 10 °C. Product inhibition studies suggest that the enzyme is able to differentiate to a high degree between the (R)-diol and (S)-diol product of the hydrolysis reaction with tert-butyl glycidyl ether as the substrate. The highest activity of the enzyme was at 42 °C and a pH of 6.8. Six peptide sequences, which were obtained by cleavage of the purified enzyme with trypsin and mass spectrometry analysis of the tryptic peptides, show high similarity with corresponding sequences originated from the epoxide hydrolase from Aspergillus niger LCP 521.
Keywords: Epoxide hydrolase; Enantioselectivity; Aspergillus niger; Substrate specificity;
Overexpression of UCP3 in both murine and human myotubes is linked with the activation of proteolytic systems: A role in muscle wasting? by Sílvia Busquets; Cèlia Garcia-Martínez; Mireia Olivan; Esther Barreiro; Francisco J. López-Soriano; Josep M. Argilés (253-258).
Overexpression of the UCP3 gene in both murine and human myotube cell cultures leads to a significant activation of the different proteolytic systems involved in muscle myofibrillar protein breakdown. Thus, lysosomal (cathepsin B) and non-lysosomal (m-calpain and ubiquitin-proteasome) mRNA content was significantly increased in the different cell culture systems used. Interestingly, the overexpression of the UCP3 gene was not associated with any changes in apoptosis. Although the function of the UCP3 protein is not completely understood (uncoupling, oxidative stress), these results suggest a possible relation between these main mechanisms involved in muscle wasting during cancer.
Keywords: UCP3; Myotube; Ubiquitin; Proteasome; Cathepsin; Calpain; Muscle wasting;
Colorectal cancer metastases affect the biochemical characteristics of the human liver β-adrenoceptor-G-protein-adenylate cyclase system by Woubet T. Kassahun; Fritz R. Ungemach; Jutta Gottschalk; Johann Hauss; Getu Abraham (259-266).
The sympathetic-catecholamine system is involved in the regulation of hepatic metabolic pathways mainly through cAMP-linked β2-adrenoceptors (β2-ARs) in humans and to a lesser extent through cAMP-independent mechanisms, but no information is available about the possible biochemical changes of β2-ARs and their signalling pathways in human colorectal cancer (CRC) and colorectal cancer hepatic metastases (CRCHM). Changes in density and distribution of β-ARs as well as in post-receptor signalling components were studied in membranes of human liver with CRCHM, and for comparison, in membranes of nonadjacent, non-metastatic human liver (NA-NM) obtained from 13 patients, using binding and competition binding studies. Studies were also carried out using normal and cancerous human colon tissues. In CRCHM, the density of β-ARs (B max) was significantly reduced, compared to NA-NM liver tissues (40.09 ± 2.83 vs. 23.09 ± 3.24 fmol/mg protein; P < 0.001). A similar decrease in the β-AR density was observed in the colon with primary colorectal cancer compared to healthy colon (37.6 ± 2.2 vs. 23.8 ± 3.5 fmol/mg protein), whereas the affinity of ICYP binding to the receptor remained unaffected. Desensitized β-ARs were uncoupled from stimulatory G-protein (GS), as total density of β-adrenoceptors in the high affinity state was significantly reduced. Concomitantly, CRCHM elicited decrease in the catalytic adenylate cyclase (AC) activity (cAMP formation) in response to isoproterenol plus GTP or forskolin or NaF. In NA-NM and CRCHM liver, the inhibition–concentration curves of ICI 118.551 showed the presence of a homogeneous population of the β2-AR subtypes. Neither the binding patterns nor the inhibition constant (K i) of ICI 118.551 were altered in CRCHM. In CRCHM, the hepatic β-AR-G-protein(s)-AC signalling system was markedly impaired, thus, these changes may well influence β-AR-mediated functions in both organs.
Keywords: Colon cancer; Liver; metastasis; β-adrenoceptor; Signal transduction;
The anti-cancer drug, doxorubicin, causes oxidant stress-induced endothelial dysfunction by Matthew B. Wolf; John W. Baynes (267-271).
The anticancer drug doxorubicin (DOX) is toxic to target cells, but also causes endothelial dysfunction and edema, secondary to oxidative stress in the vascular wall. Thus, the mechanism of action of this drug may involve chemotoxicity to both cancer cells and to the endothelium. Indeed, we found that the permeability of monolayers of bovine pulmonary artery endothelial cells (BPAEC) to albumin was increased by ∼10-fold above control, following 24-h exposure to clinically relevant concentrations of DOX (up to 1 μM). DOX also caused >4-fold increases in lactate dehydrogenase leakage and large decreases in ATP and reduced glutathione (GSH) in BPAECs, which paralleled the increases in endothelial permeability. A large part of the ATP loss could be attributed to DOX-induced hydrogen peroxide production which inhibited key thiol-enzymes, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and glucose-6-phosphate dehydrogenase (G6PDH). Depletion of reduced nicotinamide adenine dinucleotide phosphate (NADPH) appeared to be a major factor leading to DOX-induced GSH depletion. At low concentrations, the sulfhydryl reagent, iodoacetate (IA), inhibited GAPDH, caused a decrease in ATP and increased permeability, without inhibiting G6PDH or decreasing GSH. These results, coupled with those of previous work on a related quinone, menadione, suggest that depletion of either GSH or ATP may lead independently to endothelial dysfunction during chemotherapy, contributing to the cardiotoxicity and other systemic side-effects of the drug.
Keywords: Oxidative stress; Vascular permeability; Endothelial monolayer; Doxorubicin; Menadione; Glutathione; ATP; Glyceraldehyde-3-phosphate dehydrogenase; Glucose-6-phosphate dehydrogenase;
Ionic interventions that alter the association of troponin C C-domain with the thin filaments of vertebrate striated muscle by Valeria P. Sousa; José R. Pinto; Martha M. Sorenson (272-282).
The regulatory complex of vertebrate skeletal muscle integrates information about cross-bridge binding, divalent cations and other intracellular ionic conditions to control activation of muscle contraction. Relatively little is known about the role of the troponin C (TnC) C-domain in the absence of Ca2+. Here, we use a standardized condition for measuring isometric tension in rabbit psoas skinned fibers to track TnC attachment and detachment in the absence of Ca2+ under different conditions of ionic strength, pH and MgATP. In the presence of MgATP and Mg2+, TnC detaches more readily and has a 1.5- to 2-fold lower affinity for the intact thin filament at pH 8 and 250 mM K+ than at pH 6 or in 30 mM K+; changes in affinity are fully reversible. The response to ionic strength is lost when Mg2+ and MgATP are absent, whereas the response to pH persists, suggesting that weaker electrostatic TnC–TnI–TnT interactions can be overridden by strongly bound cross-bridges. In solution, titration of a fluorescent C-domain mutant (F154W TnC) with Mg2+ reveals no significant changes in Mg2+ affinity with pH or ionic strength, suggesting that these parameters influence TnC binding by acting directly on electrostatic forces between TnC and TnI rather than by changing Mg2+ binding to C-domain sites III and IV.
Keywords: Troponin C affinity; Skinned fibers; Ionic strength; pH; Mg2+ affinity;
Anti-apoptotic activity of caffeic acid, ellagic acid and ferulic acid in normal human peripheral blood mononuclear cells: A Bcl-2 independent mechanism by Krishan Lal Khanduja; Pramod Kumar Avti; Surender Kumar; Nidhi Mittal; Kiranjit Kaur Sohi; Chander Mohan Pathak (283-289).
Polyphenols have been shown to induce apoptosis in a variety of tumor cells including leukemia both in vitro and in vivo. However, their action on normal human peripheral blood mononuclear cells (PBMCs) during oxidative stress remains to be explored. In this study, we have evaluated the anti-apoptotic and radical scavenging activities of dietary phenolics, namely caffeic acid (CA), ellagic acid (EA) and ferulic acid (FA). H2O2-induced apoptosis in normal human PBMCs was assayed by phosphotidylserine externalization, nucleosomal damage and DNA fragmentation. Incubation of PBMCs with 5 mM H2O2 led to increased Annexin-V binding to externalized phosphatidyl serine (PS), an event of pre-apoptotic stage of the cell. Peripheral blood mononuclear cells pretreated with phenolics could resist H2O2-induced apoptotic damage. Caffeic acid (60 and 120 μM) and EA (100 and 200 μM) caused no change in externalization of PS, whereas FA (100 and 200 μM) increased externalization of PS in PBMCs treated with H2O2. The effects of phenolics were abolished to a large extent by culturing the PBMCs for 24 h after washing the phenolics from the medium. Inhibitory activities of these phenolics on lipid peroxidation were in the order of EA < CA < FA. DPPH-scavenging activities of EA, CA and FA were found to be 31.2 ± 1.36, 50 ± 1.86 and 73.0 ± 1.58 μM respectively. Although, the phenolics significantly inhibited DNA damage and lipid peroxidation, they could not alter the Bcl-2 expression in PBMCs. In conclusion, the anti-apoptotic effect of EA, CA and FA in PBMCs seems to be through the Bcl-2 independent mechanism.
Keywords: Apoptosis; Bcl-2; Caffeic acid; Ellagic acid; Ferulic acid; Oxidative stress;
CLA isomers inhibit TNFα-induced eicosanoid release from human vascular smooth muscle cells via a PPARγ ligand-like action by Robert Ringseis; André Müller; Christian Herter; Susan Gahler; Hans Steinhart; Klaus Eder (290-300).
Conjugated linoleic acids (CLAs) were reported to have anti-atherogenic properties in animal feeding experiments. In an attempt to elucidate the molecular mechanisms of these anti-atherogenic effects, the modulatory potential of CLA on cytokine-induced eicosanoid production from smooth muscle cells (SMCs), which contributes to the chronic inflammatory response associated with atherosclerosis, has been investigated in the present study. cis-9, trans-11 CLA and trans-10, cis-12 CLA were shown to reduce proportions of the eicosanoid precursor arachidonic acid in SMC total lipids and to inhibit cytokine-induced NF-κB DNA-binding activity, mRNA levels of inducible enzymes involved in eicosanoid formation (cPLA2, COX-2, mPGES), and the production of the prostaglandins PGE2 and PGI2 by TNFα-stimulated SMCs in a dose-dependent manner. The effect of 50 μmol/L of either CLA isomer was as effective as 10 μmol/L of the PPARγ agonist troglitazone in terms of inhibiting the TNFα-stimulated eicosanoid production by SMCs. PPARγ DNA-binding activity was increased by both CLA isomers compared to control cells. Moreover, it was shown that the PPARγ antagonist T0070907 partially abrogated the inhibitory action of CLA isomers on cytokine-induced eicosanoid production and NF-κB DNA-binding activity by vascular SMCs suggesting that PPARγ signalling is at least partially involved in the action of CLA in human vascular SMCs. With respect to the effects of CLA on experimental atherosclerosis, our findings suggest that the anti-inflammatory effect of CLA is at least partially responsible for the anti-atherogenic effects of CLA observed in vivo.
Keywords: Conjugated linoleic acid; Atherosclerosis; Human coronary artery smooth muscle cell; Eicosanoid; TNFα; Troglitazone;