title: In vivo contribution of Class III alcohol dehydrogenase (ADH3) to alcohol metabolism through activation by cytoplasmic solution hydrophobicity.
abstract: Alcohol metabolism in vivo cannot be explained solely by the action of the classical alcohol dehydrogenase, Class I ADH (ADH1). Over the past three decades, attempts to identify the metabolizing enzymes responsible for the ADH1-independent pathway have focused on the microsomal ethanol oxidizing system (MEOS) and catalase, but have failed to clarify their roles in systemic alcohol metabolism. In this study, we used Adh3-null mutant mice to demonstrate that Class III ADH (ADH3), a ubiquitous enzyme of ancient origin, contributes to alcohol metabolism in vivo dose-dependently resulting in a diminution of acute alcohol intoxication. Although the ethanol oxidation activity of ADH3 in vitro is low due to its very high Km, it was found to exhibit a markedly enhanced catalytic efficiency (kcat/Km) toward ethanol when the solution hydrophobicity of the reaction medium was increased with a hydrophobic substance. Confocal laser scanning microscopy with Nile red as a hydrophobic probe revealed a cytoplasmic solution of mouse liver cells to be much more hydrophobic than the buffer solution used for in vitro experiments. So, the in vivo contribution of high-Km ADH3 to alcohol metabolism is likely to involve activation in a hydrophobic solution. Thus, the present study demonstrated that ADH3 plays an important role in systemic ethanol metabolism at higher levels of blood ethanol through activation by cytoplasmic solution hydrophobicity.
authors.affiliation: Department of Legal Medicine, Nippon Medical School, 1-1-5 Sendagi, Tokyo 113-8602, Japan. hasebat@nms.ac.jp
authors.forename: Takeshi
authors.initials: T
authors.lastname: Haseba
authors.forename: Gregg
authors.initials: G
authors.lastname: Duester
authors.forename: Akio
authors.initials: A
authors.lastname: Shimizu
authors.forename: Isao
authors.initials: I
authors.lastname: Yamamoto
authors.forename: Kouji
authors.initials: K
authors.lastname: Kameyama
authors.forename: Youkichi
authors.initials: Y
authors.lastname: Ohno
mesh_terms: D000426:Alcohol Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D003593:Cytoplasm / Q000737:chemistry*; D004789:Enzyme Activation; D000431:Ethanol / Q000378:metabolism* / Q000494:pharmacology; D057927:Hydrophobic and Hydrophilic Interactions; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism*; D008099:Liver / Q000737:chemistry / Q000166:cytology / Q000378:metabolism; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D010084:Oxidation-Reduction
chemical_list: D007527:Isoenzymes; D000431:Ethanol; D000426:Alcohol Dehydrogenase