Microsomal Alcohol Oxygenase: Purification and Characterization of a Cytochrome P450 Responsible for Oxidation of 7-Hydroxy-Δ8-tetrahydrocannabinol to 7-Oxo-Δ8-tetrahydrocannabinol in Guinea Pig Liver

Guinea pig hepatic enzyme, microsomal alcohol oxygenase, was able to oxidize both 7α- and 7β-hydroxyΔ8-tetrahydrocannabinol (7α- and 7β-hydroxy-Δ8-THC) to 7-oxo-Δ8-THC. A cytochrome P450, named P450GPF-B, which mediates this oxidative metabolism was purified from hepatic microsomes of untreated female guinea pigs. The purified enzyme showed a single protein band of molecular mass 50,000 on sodium dodecyl sulfate–polyacrylamide gel electrophoresis. The NH2-terminal amino acid sequence of P450GPF-B is highly homologous with those of several cytochrome P450s belonging to the CYP3A subfamily.18O derived from atmospheric oxygen was incorporated into 31 and 6%, respectively, of 7-oxo-Δ8-THC formed from 7α- and 7β-hydroxy-Δ8-THC when the substrates were incubated with P450GPF-B under18O2. The antibody against P450GPF-B significantly suppressed the oxidative activities of 7α- and 7β-hydroxy-Δ8-THC to 7-oxo-Δ8-THC in hepatic microsomes of guinea pig. These results indicate that P450GPF-B is a major enzyme responsible for the hepatic microsomal alcohol oxygenase activities in the guinea pig.