Microsomal Aldehyde Oxygenase (MALDO): Purification and Characterization of a Cytochrome P450 Isozyme Responsible for Oxidation of 9-Anthraldehyde to 9-Anthracenecarboxylic Acid in Monkey Liver

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Oxidative activity of 9-anthraldehyde (9-AA) to 9-anthracenecarboxylic acid in monkey liver was mainly located in microsomes. The reaction required NADPH as an essential cofactor and was significantly inhibited by SKF 525-A, metyrapone, disulfiram, and CO, potent inhibitors of microsomal aldehyde oxygenase (MALDO). Two cytochrome P450 isozymes, named P450JM-A and P450JM-C, which mediate the oxidative biotransformation of 9-AA were purified from hepatic microsomes of untreated male and female Japanese monkeys, respectively. These isozymes each showed a single band of molecular mass 51, 000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The NH₂-terminal amino acid sequences of P450JM-A and P450JM-C are highly homologous with those of several P450s belonging to the CYP2A and CYP2B subfamilies, respectively. The anti-P450JM-C antibody significantly suppressed 9-AA MALDO activity in monkey liver, but antiP450JM-A antibody did not. The antibody against CYP2C11, which is a major isozyme responsible for 9-AA MALDO in male rat liver, also inhibited the activity. These results indicate that P450JM-C and isozyme (s) immunologically related to CYP2C11 predominantly possess MALDO activity toward 9-AA.