The metabolic role of human ADH3 functioning as ethanol dehydrogenase.
Human class III alcohol dehydrogenase (ADH3), also known as glutathione-dependent formaldehyde dehydrogenase, exhibited non-hyperbolic kinetics with ethanol at a near physiological pH 7.5. The S(0.5) and k(cat) were determined to be 3.4+/-0.3 M and 33+/-3 min(-1), and the Hill coefficient (h) 2.21+/-0.09, indicating positive cooperativity. Strikingly, the S(0.5) for ethanol was found to be 5.4 x 10(6)-fold higher than the K(m) for S-(hydroxymethyl)glutathione, a classic substrate for the enzyme, whereas the k(cat) for the former was 41% lower than that for the latter. Isotope effects on enzyme activity suggest that hydride transfer may be rate-limiting in the oxidation of ethanol. Kinetic simulations using the experimentally determined Hill constant suggest that gastric ADH3 may highly effectively contribute to the first-pass metabolism at 0.5-3 M ethanol, an attainable range in the gastric lumen during alcohol consumption. The positive cooperativity mainly accounts for this metabolic role of ADH3.
Lee
Shou-Lun
SL
Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 114, Taiwan. yinsj@ndmc.idv.tw
Wang
Ming-Fang
MF
Lee
An-I
AI
Yin
Shih-Jiun
SJ
D000426:Alcohol Dehydrogenase / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D000431:Ethanol / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D016014:Linear Models; D008099:Liver / Q000201:enzymology; D011485:Protein Binding; D011994:Recombinant Proteins / Q000737:chemistry; D013270:Stomach / Q000201:enzymology; D013997:Time Factors
D011994:Recombinant Proteins; D000431:Ethanol; C420272:ADH1C protein, human; D000426:Alcohol Dehydrogenase