Mammalian alcohol dehydrogenase: characteristics of class III isoenzymes

The kinetic characteristics of alcohol dehydrogenase class III have been studied using class III isoenzymes purified from human liver (X-ADH) and rat liver (ADH-2). Our results confirm that long chain primary alcohols and aldehydes are the best substrates, although some aromatic compounds can also be actively metabolized. Kinetic analysis suggests an ordered bibi mechanism for X-ADH. Ethanol can be oxidized by class III isoenzymes at high substrate concentration, but with a very slow rate. Thus, their contribution to physiological ethanol elimination is probably insignificant. The general properties of the class III isoenzymes isolated from different mammals by ourselves and other authors are discussed.