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Concept: Alcohol dehydrogenase

173

The microaerophilic parasite Trichomonas vaginalis is a causative agent of painful vaginitis or urethritis, termed trichomoniasis, and can also cause preterm delivery or stillbirth. Treatment of trichomoniasis is almost exclusively based on the nitroimidazole drugs metronidazole and tinidazole. Metronidazole resistance in T. vaginalis does occur and is often associated with treatment failure. In most cases, metronidazole-resistant isolates remain susceptible to tinidazole, but cross resistance between the two closely related drugs can be a problem. In this study we measured activities of thioredoxin reductase and flavin reductase in four metronidazole-susceptible and five metronidazole-resistant isolates. These enzyme activities had been previously found to be downregulated in T. vaginalis with high-level metronidazole resistance induced in the laboratory. Further, we aimed at identifying factors causing metronidazole resistance and compared the protein expression profiles of all nine isolates by application of two-dimensional gel electrophoresis (2DE). Thioredoxin reductase activity was nearly equal in all strains assayed but flavin reductase activity was clearly down-regulated, or even absent, in metronidazole-resistant strains. Since flavin reductase has been shown to reduce oxygen to hydrogen peroxide, its down-regulation could significantly contribute to the impairment of oxygen scavenging as reported by others for metronidazole-resistant strains. Analysis by 2DE revealed down-regulation of alcohol dehydrogenase 1 (ADH1) in strains with reduced sensitivity to metronidazole, an enzyme that could be involved in detoxification of intracellular acetaldehyde.

Concepts: Protein, Oxygen, Alcohol, Molecular biology, Enzyme, Gel electrophoresis, Alcohol dehydrogenase, Trichomonas vaginalis

172

In this work, a simple method for alcohol synthesis with high enantiomeric purity was proposed. For this, colloidal gold and silver surface modifications with 3-mercaptopropanoic acid and cysteamine were used to generate carboxyl and amine functionalized gold and silver nanoparticles of 15 and 45 nm, respectively. Alcohol dehydrogenase from Thermoanaerobium brockii (TbADH) and its cofactor (NADPH) were physical and covalent (through direct adsorption and using cross-linker) immobilized on nanoparticles' surface. In contrast to the physical and covalent immobilizations that led to a loss of 90% of the initial enzyme activity and 98% immobilization, the use of a cross-linker in immobilization process promoted a loss to 30% of the initial enzyme activity and >92% immobilization. The yield of NADPH immobilization was about 80%. The best results in terms of activity were obtained with Ag-citr nanoparticle functionalized with carboxyl groups (Ag-COOH), Au-COOH(CTAB), and Au-citr functionalized with amine groups and stabilized with CTAB (Au-NH2(CTAB)) nanoparticles treated with 0.7% and 1.0% glutaraldehyde. Enzyme conformation upon immobilization was studied using fluorescence and circular dichroism spectroscopies. Shift in ellipticity at 222 nm with about 4 to 7 nm and significant decreasing in fluorescence emission for all bioconjugates were observed by binding of TbADH to silver/gold nanoparticles. Emission redshifting of 5 nm only for Ag-COOH-TbADH bioconjugate demonstrated change in the microenvironment of TbADH. Enzyme immobilization on glutaraldehyde-treated Au-NH2(CTAB) nanoparticles promotes an additional stabilization preserving about 50% of enzyme activity after 15 days storage. Nanoparticles attached-TbADH-NADPH systems were used for enantioselective (ee > 99%) synthesis of (S)-7-hydroxy-2-tetralol.

Concepts: Alcohol, Amine, Enzyme, Nanotechnology, Chirality, Gold, Alcohol dehydrogenase, Immobilized enzyme

32

Paleogenetics is an emerging field that resurrects ancestral proteins from now-extinct organisms to test, in the laboratory, models of protein function based on natural history and Darwinian evolution. Here, we resurrect digestive alcohol dehydrogenases (ADH4) from our primate ancestors to explore the history of primate-ethanol interactions. The evolving catalytic properties of these resurrected enzymes show that our ape ancestors gained a digestive dehydrogenase enzyme capable of metabolizing ethanol near the time that they began using the forest floor, about 10 million y ago. The ADH4 enzyme in our more ancient and arboreal ancestors did not efficiently oxidize ethanol. This change suggests that exposure to dietary sources of ethanol increased in hominids during the early stages of our adaptation to a terrestrial lifestyle. Because fruit collected from the forest floor is expected to contain higher concentrations of fermenting yeast and ethanol than similar fruits hanging on trees, this transition may also be the first time our ancestors were exposed to (and adapted to) substantial amounts of dietary ethanol.

Concepts: Protein, Alcohol, Natural selection, Metabolism, Enzyme, Yeast, Alcohol dehydrogenase, Charles Darwin

29

This review focuses on 27 studies employing experimental alcohol self-administration (ASA) in humans which were published between 1989 and 2010. Twelve studies enrolling healthy, non-dependent social drinkers (HSD) were aimed at evaluating physiological and behavioral determinants of alcohol-induced reward or modeling situations of increased risk to develop alcohol use disorders. The remaining 15 studies tested the effect of medications such as naltrexone, nalmefene, nicotine, mecamylamine, varenicline, gabapentin, aripiprazole, and rimonabant on ASA. The participants were either HSD or non-treatment-seeking alcoholics (NTSA). In 25 of these studies, the subjects ingested alcohol orally and reached a mean peak blood alcohol concentration (BAC) during baseline conditions between 43 and 47 mg% (0.043-0.047%). Two recent studies employed computer-assisted self-infusion of ethanol (CASE), where subjects press a button to request multiple sequential alcohol exposures intravenously instead of drinking. This method has been demonstrated to be safe and provides increased experimental control of BAC and keeps subjects blind concerning the amount already self-administered. Peak exposures in the CASE studies ranged from 60 to 80 mg% in HSD and up to 240 mg% in NTSA.

Concepts: Alcohol, Ethanol, Alcoholism, Alcohol abuse, Alcohol dehydrogenase, Nicotinic acetylcholine receptor, Blood alcohol content, Hangover

28

Haloarchaeal alcohol dehydrogenases are exciting biocatalysts with potential industrial applications. In this study, two alcohol dehydrogenase enzymes from the extremely halophilic archaeon Haloferax volcanii (HvADH1 and HvADH2) were homologously expressed and subsequently purified by immobilized metal-affinity chromatography. The proteins appeared to copurify with endogenous alcohol dehydrogenases, and a double Δadh2 Δadh1 gene deletion strain was constructed to prevent this occurrence. Purified HvADH1 and HvADH2 were compared in terms of stability and enzymatic activity over a range of pH values, salt concentrations, and temperatures. Both enzymes were haloalkaliphilic and thermoactive for the oxidative reaction and catalyzed the reductive reaction at a slightly acidic pH. While the NAD(+)-dependent HvADH1 showed a preference for short-chain alcohols and was inherently unstable, HvADH2 exhibited dual cofactor specificity, accepted a broad range of substrates, and, with respect to HvADH1, was remarkably stable. Furthermore, HvADH2 exhibited tolerance to organic solvents. HvADH2 therefore displays much greater potential as an industrially useful biocatalyst than HvADH1.

Concepts: Protein, Alcohol, Metabolism, Enzyme, Ethanol, Catalysis, PH, Alcohol dehydrogenase

27

This work aims to establish microscale methods to rapidly explore bioprocess options that might be used to enhance bioconversion reaction yields: either by shifting unfavourable reaction equilibria or by overcoming substrate and/or product inhibition. As a typical and industrially relevant example of the problems faced we have examined the asymmetric synthesis of (2S,3R)-2-amino-1,3,4-butanetriol from L-erythrulose using the ω-transaminase from Chromobacterium violaceum DSM30191 (CV2025 ω-TAm) and methylbenzylamine as the amino donor. The first process option involves the use of alternative amino donors. The second couples the CV2025 ω-TAm with alcohol dehydrogenase and glucose dehydrogenase for removal of the acetophenone (AP) by-product by in situ conversion to ®-1-phenylethanol. The final approaches involve physical in-situ product removal methods. Reduced pressure conditions, attained using a 96-well vacuum manifold were used to selectively increase evaporation of the volatile AP while polymeric resins were also utilised for selective adsorption of AP from the bioconversion medium. For the particular reaction studied here the most promising bioprocess options were use of an alternative amino donor, such as isopropylamine, which enabled a 2.8-fold increase in reaction yield, or use of a second enzyme system which achieved a 3.3-fold increase in yield.

Concepts: Alcohol, Amino acid, Amine, Enzyme, Carcinoma in situ, Aza-Baylis-Hillman reaction, In situ, Alcohol dehydrogenase

26

2-Butanol and its chemical precursor butanone (methyl ethyl ketone - MEK) are chemicals with potential uses as biofuels and biocommodity chemicals. In order to produce 2-butanol, we have demonstrated the utility of using a TEV-protease based expression system to achieve equimolar expression of the individual subunits of the two protein complexes involved in the B12-dependent dehydratase step (from the pdu-operon of Lactobacillus reuterii), which catalyze the conversion of meso-2,3-butanediol to butanone. We have furthermore identified a NADH dependent secondary alcohol dehydrogenase (Sadh from Gordonia sp.) able to catalyze the subsequent conversion of butanone to 2-butanol. A final concentration of 4±0.2 mg/L 2-butanol and 2±0.1 mg/L of butanone was found. A key factor for the production of 2-butanol was the availability of NADH, which was achieved by growing cells lacking the GPD1 and GPD2 isogenes under anaerobic conditions.

Concepts: Alcohol, Metabolism, Enzyme, Ethanol, Yeast, Alcohol dehydrogenase, Beer, Butanone

26

Glucose dehydrogenases have been highly promoted to high-accuracy blood glucose (BG) monitors. The flavin adenine dinucleotide glucose dehydrogenase (FAD-GDH) and mutant variant of quinoprotein glucose dehydorgenase (Mut. Q-GDH) are widely used in high-performance BG monitors for multi-patient use. Therefore we conducted accuracy evaluation of the GDH monitors, FAD-GDH-based GM700 and Mut. Q-GDH-based Performa.

Concepts: Adenosine triphosphate, Blood sugar, Adenine, Blood glucose monitoring, Alcohol dehydrogenase, Dehydrogenase, FAD, Riboflavin

23

Isobutanol is a valuable chemical and is considered a new generation biofuel. Construction of isobutanol synthesis pathways in bacteria is a hot topic in isobutanol production. Here, we show that an isobutanol synthesis pathway exists naturally in Klebsiella pneumoniae; however, this pathway is dormant in the wild-type bacterium. K. pneumoniae is a 2,3-butanediol producer, and the synthesis pathways of 2,3-butanediol, valine and isobutanol all start from condensation of two pyruvate molecules to yield α-acetolactate. Inactivation of α-acetolactate decarboxylase (encoded by budA) resulted in α-acetolactate flowing into the valine pathway, which led to synthesis of isobutanol and 2-ketoisovalerate (a precursor of isobutanol). ldhA (lactate dehydrogenase) deletion further increased the isobutanol and 2-ketoisovalerate production. In the first step of this pathway, BudB (α-acetolactate synthase) was identified as responsible for most of the α-acetolactate synthesis. Complementation of ilvBN or ilvIH (isoenzymes of budB) both resulted in a remarkable increase in 2-ketoisovalerate production. Thus, α-acetolactate formation is the rate-limiting step of 2-ketoisovalerate production. ilvC (acetohydroxy acid isomeroreductase) and ilvD (dihydroxy acid dehydratase) were identified responsible for 2-ketoisovalerate synthesis from α-acetolactate. ipdC, which encodes an indole-3-pyruvate decarboxylase, was identified responsible for most of the isobutyraldehyde formation from 2-ketoisovalerate, and isobutanol production was increased 15.7 fold in the ipdC complementation strain, with a final titer of 2.45g/L. Isobutanol dehydrogenase activity is distributed across multiple alcohol dehydrogenase enzymes expressed by K. pneumoniae. BudC, DhaT, DhaD and YqhD all had isobutanol dehydrogenase activity in vitro. YqhD uses NADPH as the coenzyme, while the other dehydrogenases use NADH. However, inactivating one or two of these dehydrogenases had no effect on isobutanol production in vivo with isobutyraldehyde as the substrate. These results reveal a novel method for biological production of isobutanol and 2-ketoisovalerate.

Concepts: Enzyme, In vivo, In vitro, Alcohol dehydrogenase, Lactate dehydrogenase, Dehydrogenase, Klebsiella pneumoniae, Klebsiella

17

The objective of this study was to determine whether environmental and genetic alterations of neuronal aldehyde dehydrogenase (ALDH) enzymes were associated with increased Parkinson disease (PD) risk in an epidemiologic study.

Concepts: Epidemiology, Cancer, Disease, Infectious disease, Parkinson's disease, Alcohol dehydrogenase, Dopamine, Aldehyde dehydrogenase