Metabolic activation of phenacetin and phenetidine by several forms of cytochrome P-450 purified from liver microsomes of rats and hamsters.
Metabolic activation of phenacetin by liver microsomes proceeds via both phenetidine and N-hydroxyphenacetin to direct-acting mutagens, i.e., N-hydroxyphenetidine and p-nitrosophenetole. Five different molecular species of cytochrome P-450 have been purified from liver microsomes of drug-pretreated Wistar rats or Syrian hamsters and their abilities to activate phenetidine and phenacetin were compared using reconstituted microsome systems. High-spin forms of cytochrome P-450 purified from 3-methylcholanthrene-pretreated rats (MC-P-448-H) or hamsters (P-488 ham-II) showed higher catalytic activity for N-hydroxylation of phenetidine than three other low-spin forms of cytochrome P-450 purified from the same animals or from phenobarbital-pretreated rats. MC-P-448-H and P-488 ham-II required the presence of cytochrome b5 for their maximum activities in the reconstituted system. The five forms of cytochrome P-450, however, exhibited no measurable activity for N-hydroxylation of phenacetin either with or without cytochrome b5. The mutagenicity of phenacetin and phenetidine toward Salmonella typhimurium TA100 was generated when the reconstituted microsomes containing MC-P-488-H or P-488 ham-II were used as activating enzymes. From these results, it was suggested that high-spin forms of cytochrome P-450 (MC-P-448-H and P-448 ham-II) played an important role in the metabolic activation of phenacetin to the direct-acting mutagens.
D000627:Aminophenols / Q000378:metabolism*; D000818:Animals; D001711:Biotransformation; D055598:Chemical Phenomena; D002621:Chemistry; D006224:Cricetinae; D003577:Cytochrome P-450 Enzyme System / Q000032:analysis / Q000494:pharmacology*; D006900:Hydroxylation; D008297:Male; D008647:Mesocricetus; D008862:Microsomes, Liver / Q000201:enzymology*; D009153:Mutagens / Q000378:metabolism; D010615:Phenacetin / Q000378:metabolism*; D010628:Phenetidine / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D000627:Aminophenols; D009153:Mutagens; D010628:Phenetidine; D003577:Cytochrome P-450 Enzyme System; D010615:Phenacetin