Interaction of carbohydrates with alcohol dehydrogenase: Effect on enzyme activity

Conjugation of haloalkane dehalogenase DhaA with arabinogalactan to increase its stability

Haloalkane dehalogenase DhaA can catalyze the hydrolytic cleavage of carbonhalogen bonds, along with production of the corresponding alcohol, a proton and a halide. However, DhaA suffers from poor environmental tolerance, such as sensitivity to high temperature, low pH and hypersaline. Arabinogalactan (AG) is a hydrophilic polysaccharide with highly branched long chains. DhaA was conjugated with AG to improve the environmental stability of DhaA in the present study. Each DhaA was averagely conjugated with 4∼5 AG molecules. Conjugation of AG essentially maintained the enzymatic activity of DhaA (91.4 %) without apparent structural alteration. The hydration layer formed by AG could reduce the solvent accessible area of DhaA and slow the protonation process, thereby improving the pH and high salt stability of DhaA. In particular, the remaining activities of the conjugate (AG-DhaA) were 35.3 % after treatment at pH4.0 for 1 h, and 80.8 % in 1 M NaCl after treatment for 16 h. As compared with DhaA, AG-DhaA showed slightly different kinetic parameters (K M of 1.90 μmol/L and k cat of 2.60 s -1).

Macromolecular crowding effects on the kinetics of opposing reactions catalyzed by alcohol dehydrogenase

In order to better understand how the complex, densely packed, heterogeneous milieu of a cell influences enzyme kinetics, we exposed opposing reactions catalyzed by yeast alcohol dehydrogenase (YADH) to both synthetic and protein crowders ranging from 10 to 550 kDa. The results reveal that the effects from macromolecular crowding depend on the direction of the reaction. The presence of the synthetic polymers, Ficoll and dextran, decrease V_max and K_m for ethanol oxidation. In contrast, these crowders have little effect or even increase these kinetic parameters for acetaldehyde reduction. This increase in V_max is likely due to excluded volume effects, which are partially counteracted by viscosity hindering release of the NAD⁺ product. Macromolecular crowding is further complicated by the presence of a depletion layer in solutions of dextran larger than YADH, which diminishes the hindrance from viscosity. The disparate effects from 25 g/L dextran or glucose compared to 25 g/L Ficoll or sucrose reveals that soft interactions must also be considered. Data from binary mixtures of glucose, dextran, and Ficoll support this “tuning” of opposing factors. While macromolecular crowding was originally proposed to influence proteins mainly through excluded volume effects, this work compliments the growing body of evidence revealing that other factors, such as preferential hydration, chemical interactions, and the presence of a depletion layer also contribute to the overall effect of crowding.

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Yeast alcohol dehydrogenase reduction of acetaldehyde is enhanced by crowding.

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Crowding effects on YADH kinetics depend on the direction of the reaction.

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Crowders like dextran can be used as a tool to elucidate enzyme mechanism.

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Excluded volume optimizes YADH hydride transfer; viscosity hinders product release.

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The presence of a depletion layer with large crowders mitigates their effects.

Promoting the treatment of crude oil alkane pollution through the study of enzyme activity

Microbes appear to play a key role in bioremediation of petroleum hydrocarbons pollution and little attention has been paid to the enzyme activity in the process of alkane bioremediation. Oil field bacterium identified as Pseudomonas synxantha LSH-7' was chosen as the tested strain. Periodically collected samples were analyzed by GC-FID (Gas Chromatography- Flame Ionization Detector) and RT-qPCR (Quantitative-Real-Time-PCR). GC-FID results showed this bacterial strain has great degradation ability on crude oil n-alkanes and RT-qPCR data indicated the differences between the three genes expression including AlkB-, Cytochromes P450-, and almA- related when grown on different-chain alkanes. Meanwhile, enzyme activity like alkane hydroxylase, alcohol dehydrogenase, dehydrogenase, protease, phosphatase, catalase and lipase were measured. Extracellular alkane hydroxylase was induced in a higher degree than intracellular in the early incubation time, alcohol dehydrogenase increased/decreased along with alkane hydroxylase, and the pH of the medium obviously decreased. Other enzymes were also described including dehydrogenase activity that reached a highest point that was slower than alcohol dehydrogenase, protease activity started multiplying after a period of culture while biomass was immediately increased, catalase activity dramatically enhanced in the presence of alkanes, phosphatase activity was closely linked to pH approximately but lipase activity was found to be moderate.

Purification of Tea Saponins and Evaluation of its Effect on Alcohol Dehydrogenase Activity

Tea saponins, extracted from a Camellia oleifera cake, were found to have a potent effect on de-alcoholic activity. To obtain highly pure tea saponins, which can better maintain the activity of alcohol dehydrogenase (ADH), this paper presents an extraction method for tea saponins using deionized water as the extraction agent and a two-stage precipitation method, including ethanol precipitation and CaO precipitation. The optimum conditions for ethanol precipitation were 95% alcohol, a duration of 1.5h and a solid/liquid ratio of 1:4; while the optimum conditions for CaO precipitation were a duration of 2h and an NH₄HCO₃/CaO ratio of 2:1. Under the optimum conditions, the content of saponins was 87.58%. The results showed that the greater the amount of tea saponins and the higher its purity, the more significant its activating effect on ADH. When the purity of tea saponins was above 75%, it activated ADH. It indicated that the de-alcoholic mechanism of tea saponins is associated with the activity of ADH. Furthermore, the study characterized the structure of tea saponins by UV absorption and Fourier Transform Infrared (FTIR) spectrometry and LC-MS.

Inhibitory effects of the dietary flavonoid quercetin on the enzyme activity of zinc(II)-dependent yeast alcohol dehydrogenase: Spectroscopic and molecular docking studies

A multispectroscopic exploration was employed to investigate the interaction between the metallo-enzyme alcohol dehydrogenase (ADH) from yeast with bioflavonoid quercetin (QTN). Here, we have characterized the complex formation between QTN and Zn²⁺ in aqueous solution and then examined the effect of such complex formation on the enzymatic activity of a zinc(II)-dependent enzyme alcohol dehydrogenase from yeast. We have observed an inhibition of enzymatic activity of ADH in presence of QTN. Enzyme inhibition kinetic experiments revealed QTN as a non-competitive inhibitor of yeast ADH. Perturbation of Circular dichroic (CD) spectrum of ADH in presence of QTN is observed due to the structural changes of ADH on complexation with the above flavonoid. Our results indicate a conformational change of ADH due to removal of Zn²⁺ present in the enzyme by QTN. This was further established by molecular modeling study which shows that the flavonoid binds to the Zn²⁺ ion which maintains the tertiary structure of the metallo-enzyme. So, QTN abstracts only half of the Zn²⁺ ions present in the enzyme i.e. one Zn²⁺ ion per monomer. From the present study, the structural alteration and loss of enzymatic activity of ADH are attributed to the complex formation between QTN and Zn²⁺.

Microbial community structure shifts are associated with temperature, dispersants and nutrients in crude oil-contaminated seawaters

This study tracked structure shifts of bacterial compositions before, during and after invading by crude oil to determine the microbial response and explore how temperature, dispersants and nutrients affect the composition of microbial communities or their activities of biodegradation in artificial marine environment. During petroleum hydrocarbons exposed, the composition and functional dynamics of marine microbial communities were altered, favoring bacteria that could utilize this rich carbon source such as the Proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes phyla. Low temperature as a dominant factor decreased bacterial richness and catabolic diversity due to abated enzymes activities in correlation with the process of biodegradation. Dispersants exerted no negative consequences on microbial composition, however, bacterial composition by the Chloroflexi, TM6, OP8, Cyanobacteria and Gemmatimonadetes phyla increased. It seemed that more frequent fertilizer application could be equally safe to bacteria and increased significantly the abundance of bacterial strains but Actinobacteria phyla decreased.