Extrahepatic, differential expression of four classes of human alcohol dehydrogenase

The amounts of mRNA expressed for different alcohol dehydrogenase (ADH) classes were determined in human tissues by Northern hybridization. ADH classes I, II, and III were expressed in all tissues. The mRNAs were highest for class I ADHs, with particularly strong signals in liver, lung, ileum, colon, and uterus. For class II ADH, such a wide tissue distribution had not been recognized previously. Expression of class III ADH was highest in testis, followed by uterus, colon, and ileum. The amounts of class I and III ADH mRNAs varied significantly, indicating that tissue-specific factors modulate the expression of these enzymes above a basal level. Class V ADH (ADH6) was not detected in any of the tissues, including stomach. This suggests that class V ADH is not identical with human stomach sigma-ADH (class IV). The results support the general proposition that ADHs are not restricted to liver and have functions other than those in ethanol oxidation.