[Biochemical and pathophysiological aspects of alcohol metabolism (author's transl)].

The metabolism of ethanol to acetaldehyde proceeds in the liver via alcohol dehydrogenase (ADH) and the microsomal ethanol oxidizing system (MEOS), whereas catalase plays no significant role. ADH is localized in the cytosol, required required NAD+ as cofactor and exhibits a pH optimum in the alkaline range and a Km of less than 2 mM for ethanol. Conversely, the MEOS resides in the endoplasmic reticulum, requires NADPH and O2, is inhibited by CO, and exhibits a Km of about 10 mM for ethanol. The microsomal system also metabolizes higher aliphatic alcohols such as butanol which is not a substrate for catalase. Moreover, it could be separated from ADH and catalase by column chromatography. The MEOS exhibits a variety of properties similar to those of other microsomal drug metabolizing enzymes and is characterized by inducibility of its activity following chronic alcohol consumption, which suggests the involvement of the microsomal system in the adaptive enhancement of ethanol clearance commonly observed in alcoholics.