Alcohol oxidation by isozyme 3a of liver microsomal cytochrome P-450

Liver microsomes from rabbits treated chronically with ethanol were solubilized and fractionated to yield a new isozyme of cytochrome P-450 in a homogeneous state. This cytochrome, designated as isozyme 3a on the basis of its relative electrophoretic mobility, is distinct from the known terminal amino acid sequences. In addition, peptide mapping by high performance liquid chromatography following trypsinolysis indicates that form 3a is a unique gene product. This cytochrome has unusually high activity in the oxidation of ethanol and other alcohols to aldehydes and in the rho-hydroxylation of aniline as compared with the other isozymes of P-450. The ethanol-oxidizing activity of isozyme 3a, which requires the presence of NADPH and NADPH-cytochrome P-450 reductase and is stimulated by the presence of phosphatidylcholine, is not due to contamination by catalase or an NAD+-or NADP+-dependent alcohol dehydrogenase.