Purification and Characterization of Two Forms of Cytochrome P-450 with ω-Hydroxylase Activities toward Prostaglandin A and Fatty Acids from Rabbit Liver Microsomes1

Abstract

Two forms of cytochrome P-450 (P-450), designated as P-450LPGA omega 1 and P-450LPGA omega 2, have been purified to specific contents of 17.9 and 11.1 nmol P-450/mg protein, respectively, from liver microsomes of rabbits treated with di(2-ethylhexyl)phthalate (DEHP), a peroxisomal proliferator. The purified P-450LPGA omega 1 and P-450LPGA omega 2 were found to have apparent molecular weights of 52,500 and 53,000, respectively. They showed absorption maxima at 451 and 450 nm in the carbon monoxide-difference spectra for their reduced forms, respectively. The two P-450s both efficiently catalyzed the omega-hydroxylation of prostaglandins A1 (PGA1) and A2 (PGA2), as well as the omega- and (omega-1)-hydroxylation of fatty acids such as laurate, myristate, and palmitate. In a reconstituted system, various metal ions such as Na+ and Mg2+ stimulated these reactions. The P-450s exhibited no detectable activity toward several xenobiotics tested. The two P-450s showed different peptide map patterns following limited proteolysis with Staphylococcus aureus V8 protease or papain. The NH2-terminal amino acid sequences (ALNPTRLPGSLSGLLQVAGL and ALSLTRLPGSFSGFLQAxGLLGLLL) of P-450LPGA omega 1 and P-450LPGA omega 2 were identical at 18/20 and 19/24 positions with that of the lung prostaglandin omega-hydroxylase from pregnant rabbits, respectively. An antibody against P-450LPGA omega 2 recognized a 52,000-53,000 molecular weight protein(s) in rabbit liver microsomes. The intensity of the immunoblot was significantly increased in liver microsomes from rabbits treated with DEHP, but not with phenobarbital or 3-methylcholanthrene.(ABSTRACT TRUNCATED AT 250 WORDS)