Substitutability of metal-binding sites in an alcohol dehydrogenase / 生物工程学报

Covalently anchoring of a ligand/metal via polar amino acid side chain(s) is often observed in metalloenzyme, while the substitutability of metal-binding sites remains elusive. In this study, we utilized a zinc-dependent alcohol dehydrogenase from Thermoanaerobacter brockii (TbSADH) as a model enzyme, analyzed the sequence conservation of the three residues Cys37, His59, and Asp150 that bind the zinc ion, and constructed the mutant library. After experimental validation, three out of 224 clones, which showed comparative conversion and ee values as the wild-type enzyme in the asymmetric reduction of the model substrate tetrahydrofuran-3-one, were screened out. The results reveal that the metal-binding sites in TbSADH are substitutable without tradeoff in activity and stereoselectivity, which lay a foundation for designing ADH-catalyzed new reactions via metal ion replacement.

RecET recombination system driving chromosomal target gene replacement in Zymomonas mobilis

Background: Zymomonas mobilis is a Gram-negative microaerophilic bacterium with excellent ethanol-producing capabilities. The RecET recombination system provides an efficient tool for direct targeting of genes in the bacterial chromosome by PCR fragments. Results: The plasmids pSUZM2a-RecET and pSUZM2a-RecE588T were first developed to co-express RecE or RecE588 and RecT for homologous recombination. Thereafter, the PCR fragments of the tetracycline resistance marker gene flanked by 60 bp of adhA (alcohol dehydrogenase I) or adhB (alcohol dehydrogenase II) homologous sequences were electroporated directly into ZM4 cells harboring pSUZM2a-RecET or pSUZM2a-RecE588T. Both adhA and adhB were replaced by the tetracycline resistance gene in ZM4, yielding two mutant strains, Z. mobilis ZM4 ΔadhA and Z. mobilis ZM4 ΔadhB. These two mutants showed varying extent of reduction in ethanol production, biomass generation, and glucose metabolism. Furthermore, enzyme activity of alcohol dehydrogenase II in Z. mobilis ZM4 ΔadhB exhibited a significant reduction compared to that of wild-type ZM4. Conclusion: This approach provided a simple and useful method for introducing mutations and heterologous genes in the Z. mobilis genome.

Gastric Autoantigenic Proteins in Helicobacter Pylori Infection

PURPOSE: This study tried to identify novel gastric autoimmune antigens that might be involved in aggravating the atrophic gastritis among patients with Helicobacter pylori infection using two-dimensional immunoblotting analysis. MATERIALS AND METHODS: Proteins from gastric mucosal antrectomy specimens and AGS cells (gastric adenocarcinoma cell lines derived from a Caucasian patient who had received no prior therapy) were 2-dimensionally immunoblotted separately with a pool of 300 sera from H. pylroi-infected patients at Gyeongsang National University Hospital. RESULTS: Thirty-eight autoantigenic proteins including alcohol dehydrogenase [NADP+], alpha enolase, gastrokine-1, gastric triacylglycerol lipase, heat shock 70 kDa protein 1, and peroxiredoxin-2 were identified in the gastric mucosal tissue. Fourteen autoantigenic proteins including programmed cell death 6-interacting protein, serum albumin and T-complex protein 1 subunit gamma were identified in the AGS cells. Albumin, alpha-enolase, annexin A3, cytoplasmic actin 1, heat shock cognate 71 kDa protein and leukocyte elastase inhibitor were commonly observed autoantigenic proteins in both gastric mucosal tissue and AGS cells. Alpha-enolase, glutathione S-transferase P, heat shock cognate 71 kDa protein, heat shock 70 kDa protein 1, human mitochondrial adenosine triphosphate synthase (ATP) subunit beta, mitochondrial 60 kDa heat shock protein, peroxiredoxin-2, 78 kDa glucose-regulated protein precursor, tyrosine-protein phosphatase non-receptor type 11 and Tryptophan-Aspartic acid (WD) repeat-containing protein 1 showed 60% or higher amino acid positivity. CONCLUSION: These newly identified gastric autoimmune antigens might be useful in the control and prevention of gastroduodenal disorders, and might be valuable in breaking the vicious circle that exists in gastroduodenal disorders if their pathophysiological roles could be understood in the progress of chronic atrophic gastritis, gastroduodenal ulcers, intestinal metaplasia, and gastric carcinogenesis.

Alcohol dehydrogenase activities and ethanol tolerance in Anastrepha (Diptera, Tephritidae) fruit-fly species and their hybrids

The ADH (alcohol dehydrogenase) system is one of the earliest known models of molecular evolution, and is still the most studied in Drosophila. Herein, we studied this model in the genus Anastrepha (Diptera, Tephritidae). Due to the remarkable advantages it presents, it is possible to cross species with different Adh genotypes and with different phenotype traits related to ethanol tolerance. The two species studied here each have a different number of Adh gene copies, whereby crosses generate polymorphisms in gene number and in composition of the genetic background. We measured certain traits related to ethanol metabolism and tolerance. ADH specific enzyme activity presented gene by environment interactions, and the larval protein content showed an additive pattern of inheritance, whilst ADH enzyme activity per larva presented a complex behavior that may be explained by epistatic effects. Regression models suggest that there are heritable factors acting on ethanol tolerance, which may be related to enzymatic activity of the ADHs and to larval mass, although a pronounced environmental effect on ethanol tolerance was also observed. By using these data, we speculated on the mechanisms of ethanol tolerance and its inheritance as well as of associated traits.

Pharmacodynamics & toxicological profile of PartySmart, a herbal preparation for alcohol hangover in Wistar rats.

BACKGROUND & OBJECTIVE: PartySmart is a herbal preparation intended for the management of alcohol hangover and other related toxic effects in clinical situation. The present study was designed to investigate the pharmacodynamics and oral toxicity of PartySmart, a herbal formulation in rats. METHODS: Effect of PartySmart on blood acetaldehyde and alcohol levels was evaluated at doses of 125, 250 and 500 mg/kg b.wt. in rats. Acute toxicity study was conducted with PartySmart at a limit test dose of 2000 mg/kg b.wt., p.o. In repeated dose 90 day study, PartySmart was administered at doses of 500 and 1000 mg/kg b.wt. once-a-day, orally throughout the study period. RESULTS: PartySmart dose-dependently decreased blood ethanol and acetaldehyde levels as compared to control. PartySmart at a dose of 500 mg/kg b.wt. significantly reduced the area under curve (AUC) of ethanol and acetaldehyde levels. It increased the hepatic alcohol dehydrogenase (ADH) at 500 mg/kg b.wt. and aldehyde dehydrogenase (ALDH) activities at doses of 250 and 500 mg/kg b.w. significantly. Acute toxicity study showed no clinical signs and pre-terminal deaths. The LD(50) of PartySmart was found to be greater than 2000 mg/kg b.wt. No significant differences in PartySmart-treated groups were observed on body weight, food intake, haematological and clinical chemistry, and organ weight ratios as compared to control group in the repeated dose study. Histopathological examination of all target organs showed no evidence of lesions attributing to drug toxicity. INTERPRETATION & CONCLUSION: PartySmart enhanced acetaldehyde metabolism by increasing ADH and ALDH activity without any side effects. These findings indicate that PartySmart may exert beneficial role in the management of alcohol hangover without any toxicity.

Postnatal development of alcohol dehydrogenase in liver and intestine of rats exposed to ethanol in utero.

BACKGROUND AND OBJECTIVES: Ethanol exposure during gestation induces marked aberrations in growth and development of offsprings collectively known as foetal alcohol syndrome (FAS);. However, its effects on the postnatal development of alcohol dehydrogenase (ADH) are not adequately investigated. Therefore, ADH activity in liver and intestine of rats exposed to ethanol during gestation was studied in relation to postnatal development. METHODS: Pregnant female rats beginning at day 1 of gestation were fed 1 ml of 30 per cent ethanol daily during the entire gestation period. ADH activity was determined in liver and intestine postnatally at day 4, 8, 14, 20 and 30. DNA and RNA contents and intestinal histology were also examined. RESULTS: During the first two weeks of postnatal life, there was no difference in ADH levels of rat liver and intestine in control and prenatally ethanol exposed pups but ADH levels were significantly reduced at 3-4 wk in ethanol fed group compared to control. A similar decrease in DNA and RNA contents of intestine and changes in tissue morphology were observed in ethanol exposed pups during postnatal development. INTERPRETATION AND CONCLUSION: The findings of our study suggested that prenatal ethanol exposure modified ADH activity in liver and intestine during postnatal development. This could affect ethanol metabolism under these conditions.

Effect of thyroid hormone on the alcohol dehydrogenase activities in rat tissues

The effects of thyroid hormone on hepatic and gastric alcohol dehydrogenase (ADH) activities (nM of NADH/min/mg of cytosolic protein) have been investigated in male Sprague Dawley rats treated with thyroxine (1 mg/kg, po) for 14 days. Whereas hepatic ADH activity in thyroxine-treated rats decreased by 61.3% of control rats (26.4 vs 43.2, p<0.001), gastric ADH activity increased by 262.9% of control rats (4.9 vs 1.9, p<0.001). As for the activities of the lung and kidney, thyroxine treatment did not produce any statistically significant changes. These data suggest that thyrotoxicosis causes a decrease of hepatic alcohol metabolism, and that the increase of gastric ADH activity in thyrotoxic rats can partly restore the first-pass metabolism of ethanol.

Enzymology of ethanol and acetaldehyde metabolism in mammals

Ehtanol or wthyl alcohol is a molecule that, in mammals, is naturally present at low concentrations due to its production by gastrointestinal flora fermentation activity. However, it is remarkable that this metabolite, with a clearly minor role in regular vertebrate metabolism, can be oxidized into acetaldehyde through several ensymatic and non-enzymatic mechanisms, which comprise the activity of more than ten ensymes and isozymes, many of them broadly distributed in different specie and tissues. In correspondence, acetaldehyde can also be oxidized into acetate through several enzymatic pathways that involve about ten enzymes and isozymes which also have a broad distribution In this article, a complete review of the aforementioned metabolic pathways is elaborated. From this group, the participation and wide distribution of alcohol dehydrogenase and aldehyde dehydrogenase systems are emphasized. The mechanism of reaction, kinetic characteristics and physiological relevance are described, and finally, the possible physiological role of these enzymatic systems as responsible to synthesize or catabolize several endogenous metabolites that regulate growth, metabolism, differentiation and neuroendocrine function in mammals are discussed

Isolation of NADH from Saccharomyces cerevisiae by ether permeabilization and its purification by affinity ultrafiltration.

Cells of Saccharomyces cerevisiae were permeabilized by ether for the isolation of coenzyme NADH. A 4-fold increase in the ether fraction to aqueous fraction resulted in the recovery of 80% of total NADH present in the cell. NADH was separated and purified by affinity ultrafiltration using yeast alcohol dehydrogenase as an affinity ligand. The binding characteristics of the enzyme and coenzyme were established at different pH and ionic strengths using gel filtration. The number of moles of NADH bound per mole of alcohol dehydrogenase (r) was found to be 5.7 at pH 8 and ionic strength (I) 0.1 M. The binary complex of NADH and alcohol dehydrogenase was cleaved by lowering the pH to 6.0. The crude cell permeate on purification by ultrafiltration with 2-fold dilution, gave NADH with an absorbance ratio (A260/A340) of 2.3 and overall yield of 68%. Alcohol dehydrogenase was recovered as retentate with 93% recovery and 15% loss in activity.

Alcohol dehydrogenase activity in mouse brown adipose tissue.

The present work provides evidence for the occurrence of the enzyme alcohol dehydrogenase (ADH) in very minute concentration in mice brown adipose tissue (BAT). Mice consuming 10% ethanol for 10 days showed significantly lowered enzyme activity in brown fat while liver ADH activity was increased but not significantly. Measurements of basal and norepinephrine stimulated oxygen consumption of isolated brown adipocytes indicated that the presence of ADH in BAT of mice is unlikely to play any role in ethanol oxidation.

Kinetic mechanism of yeast alcohol dehydrogenase activity with secondary alcohols and ketones.

The kinetic mechanism of yeast alcohol dehydrogenase (EC 1.1.1.1) activity with the redox pair 2-propanol/acetone has been probed in detail by the application of initial rate studies in the absence and in the presence of products, and a dead-end inhibitor pyrazole. An overall steady-state random Bi Bi mechanism in both directions, with the formation of both abortive ternary complexes, enzyme.NADH.2-propanol and enzyme.NAD+.acetone has been observed. A complete list of steady-state kinetic constants are also reported for the redox pair (S)-(+)-2-butanol/2-butanone.

Stability and kinetic behaviour of some enzymes in surfactant environment.

The interaction of alpha-chymotrypsin, invertase, alcohol dehydrogenase and alkaline phosphatase with some ionic and non-ionic surfactants, viz. sodium dodecyl sulphate, dioctyl sodium sulphosuccinate, hexadecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide and Triton X-100, has been examined by studying the effect of varying surfactant concentrations on enzyme activities as well as by determining the time-dependent inactivation and the time-independent inhibition. The kinetic parameters, Km and Vmax, for alpha-chymotrypsin-catalysed reaction in presence of sodium dodecyl sulphate were evaluated. Anionic surfactants markedly decreased enzyme activity, whereas cationic surfactants were less effective. Nonionics showed no effect. This change in enzyme activity was also dependent on the nature of enzyme.

Effect of substrates and coenzymes on the molecular symmetry-related properties of horse liver and yeast alcohol dehydrogenases.

Thermal inactivation of horse liver alcohol dehydrogenase (LADH) exhibits the following biphasic kinetics A = Afast.e-Kfast.t + Aslow.e-Kslow.t Where A is the per cent residual activity at time t,Afast and Aslow are amplitudes (expressed as % of initial activity) and kfast and kslow first-order rate constants of the fast and slow phases, respectively. For apoenzyme, Afast = Aslow = 50% of the initial activity under all conditions of temperature and pH. On the addition of a substrate or coenzyme ligand, there is a ligand concentration-dependent increase in per cent Aslow and a decrease in kslow. At sufficiently high ligand concentration, the entire time-course of inactivation can be described as a single exponential decay. The variations of per cent Aslow and of kslow with ligand concentration are consistent with the existence of two binding sites of different ligand affinities. Inactivation of LADH by excess EDTA also exhibits a similar biphasic kinetics with Afast = Aslow = 50% of the initial activity. Addition of ethanol or NAD+ brings about a concentration-dependent decrease in kfast and kslow without affecting amplitudes of the two phases. The NAD+ concentration-dependence of this decrease is consistent with a single dissociation constant for the coenzyme. Inactivation of yeast alcohol dehydrogenase by heat or excess EDTA can be represented as a single exponential decay of activity under all conditions of temperature and pH in the absence as well as presence of ethanol or NAD+. Implications of these results for the molecular symmetry of the two oligomeric enzymes in solution are discussed.