Isolation of Cytochrome P-450 Highly Active in Prostaglandin ω-Hydroxylation from Lung Microsomes of Rabbits Treated with Progesterone1

Abstract

Two forms of cytochrome P-450, designated as cytochrome P-450p-1 and cytochrome P-450p-2, were separated and purified to specific contents of 8.2 and 8.9 nmol/mg of protein, respectively, from lung microsomes of rabbits treated with progesterone. Cytochrome P-450p-1 and cytochrome P-450p-2 migrated as single polypeptide bands with molecular weights of 49,000 and 52,000, respectively, on SDS-polyacrylamide gel. Their CO-reduced difference spectral peaks were at 451.5 and 450 nm, respectively. Cytochrome P-450p-1 catalyzed the N-demethylation of benzphetamine, O-demethylation of p-nitroanisole, and O-deethylation of 7-ethoxycoumarin, whereas no activity was observed with cytochrome P-450p-2. On the other hand, cytochrome P-450p-2 catalyzed the omega-hydroxylation of prostaglandin E1 (PGE1), prostaglandin E2 (PGE2), and prostaglandin A1 (PGA1) with turnover rates of 9.0, 7.5, and 5.0 nmol of product/min/nmol of cytochrome P-450, respectively, as well as the omega- and (omega-1)-hydroxylation of palmitate and myristate with turnover rates of 27.7 and 16.4 nmol products/min/nmol of cytochrome P-450, respectively. This cytochrome showed a greater affinity for prostaglandins (PGs) than for fatty acids. These reactions were absolutely dependent on cytochrome P-450p-2 and NADPH-cytochrome P-450 reductase, and stimulated by addition of phosphatidylcholine and cytochrome b5. Cytochrome P-450p-2 is thought to be a new form of cytochrome P-450 induced by progesterone treatment in rabbit lung microsomes.