Guinea pig liver alcohol dehydrogenase: isolation and characterization of two distinct classes of isozymes.

1. Two distinct classes of alcohol dehydrogenase (ADH) isozymes were purified from guinea pig liver. 2. While the two classes of isozymes have similar subunit weight and electrophoretic mobility on starch gel, they differ markedly in catalytic properties. 3. The class A ADH oxidizes rapidly, exhibits saturated kinetics with both primary and secondary alcohols and is inhibited very effectively by 4-methylpyrazole (Ki = 0.58 microM) and o-phenanthroline (I50 = 0.1 mM). 4. The class B isozyme does not oxidize secondary alcohols, exhibits saturated kinetics only with long chain primary alcohols and is less sensitive to the ADH inhibitors 4-methylpyrazole (Ki = 15 mM) and o-phenanthroline (I50 greater than 10 mM).