Microsomal Ethanol Oxidation: Activity in Vitro and in Vivo

The oxidation of ethanol to acetaldehyde by components of the microsomal fraction of mammalian liver has been proposed as a route of alcohol metabolism ancillary to the alcohol dehydrogenase pathway (1, 2, 3, 4, 5). First reported by Orme-Johnson and Ziegler in 1965 (6), the in vitro reaction has since been examined in a number of laboratories. These studies have produced conflicting opinions of the enzymic mechanism, however. Initially, the reaction was thought to be mediated by the hepatic microsomal drug detoxification enzymes in a mechanism that did not involve either of the known alcohol oxidizing enzymes, alcohol dehydrogenase or catalase (1, 2, 6). The possibility of a mutual pathway for the metabolism of alcohol and other drugs stimulated great interest in this process. Later evidence indicated, however, that the reaction was hydrogen peroxide dependent, and it was suggested that catalase,as a contaminant of the microsomes, was the enzyme responsible for the conversion of ethanol to acetaldehyde (7, 8, 9, 10).