Purification and properties of a cytochrome P450 arachidonic acid epoxygenase from rabbit renal cortex

A rabbit cytochrome P450 which catalyzes the epoxidation of arachidonic acid to two of the four possible regioisomeric epoxyeicosatrienoic acid metabolites was purified from renal cortex. A small amount of the unresolved omega/omega-1 hydroxylated eicosatetraenoic acid products were also produced. The enzyme had a specific content of 8.4 nmol of P450/mg of protein and exhibited a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis after silver staining. Sequencing revealed a single NH2-terminal amino acid sequence with the first 20 residues identical to rabbit cytochrome P450 2C2. We suggest this enzyme be termed P450 2CAA (for arachidonic acid) until the complete sequence and substrate selectivity are established. Purified P450 2CAA was in the low spin state as evidenced by an absorption maximum at 415 nm; the reduced-carbonyl complex exhibited a maximum at 451 nm. The specific activity for metabolism of 7 microM arachidonic acid was 1.1 nmol of product formed/min/nmol of P450. About 75% of the metabolites were two of the four possible epoxyeicosatrienoic acids identified as the 11,12- and 14,15-epoxyeicosatrienoic acids by coelution with synthetic and commercial standards on reversed and normal-phase high pressure liquid chromatographic separations. The ratio of the 11,12- to 14,15-epoxyeicosatrienoic acids was 1.5:1. The purified enzyme exhibited no significant activity toward 7-ethoxyresorufin or progesterone, but demethylated aminopyrine and benzphetamine. Other fatty acids were also substrates for the enzyme. Oleic, linoleic, and lauric acids, all at about 10 microM, were metabolized at rates of 0.32, 0.72, and 0.73 nmol/min/nmol of P450, respectively. Monoclonal antibody that cross-reacts with P450 2C2 inhibited 63% of the microsomal epoxidation activity from renal cortex microsomes from phenobarbital-treated rabbits. The production of the epoxide metabolites of arachidonic acid suggests that P450 2CAA may have a significant role in arachidonic acid-mediated intra- and intercellular signalling pathways.