ABSTRACT
Alcohol dehydrogenase (ADH) exhibits multiple forms in humans. At protein level, four ADH classes (I-IV) have been identified in human tissues, while an additional class (V) has been detected at the mRNA level (1). Human ADH classes I, II, and IV exhibit appropriate kinetic constants for an effective ethanol metabolism at the blood ethanol concentrations attained after social drinking (2). Class III activity with ethanol is detected only at very high concentrations (>100 mM) and, therefore, its contribution to ethanol metabolism should normally be minimal. The presence of ADH classes I, II, or IV in a tissue indicates an active ethanol metabolism after consumption of alcoholic beverages. Most ADH activity in the human body is concentrated in liver, due to high content of classes I and II (about 3% of the hepatic soluble protein). However, many organs other than liver exhibit a detectable ADH activity, because of the presence of classes I and/or IV—at the protein level, class II has been detected only in liver and skin (3). The contribution of extrahepatic organs to ethanol metabolism is small but significant. The study of the activity and ADH forms of each organ should serve to estimate the amount of local ethanol metabolism, and the consequent production of acetaldehyde and increase in NADH concentration. This may have pathological consequences and may explain some of the effects of ethanol in the organ.
