Mechanism of inhibition by carbonyl cyanide m-chlorophenylhydrazone and sodium deoxycholate of cytochrome P-450-catalysed hepatic microsomal drug metabolism.
1. Treatment of liver microsomal fraction with 0.03-0.12% sodium deoxycholate and 0.005-0.06 mM carbonyl cyanide m-chlorophenylhydrazone decreases phospholipid-dependent hydrophobicity of the microsomal membrane, assayed by the kinetics of 8-anilinonaphthalene-1-sulphonate binding and ethyl isocyanide difference spectra. 2. Sodium deoxycholate at a concentration of 0.01% lacks its detergent properties, but competitively inhibits aminopyrine binding and activates the initial rate of NADPH-cytochrome P-450 reductase. In the presence of 0.03-0.09% sodium deoxycholate the rate-limiting factor in p-hydroxylation of aniline is the content of cytochrome P-450. and that for N-demethylation of aminopyrine is the activity of NADPH-cytochrome P-450 reductase. 3. Carbonyl cyanide m-chlorophenylhydrazone has no effect on the binding and metabolism of aniline; investigation of its inhibiting effect on aminopyrine N-demethylase established that the rate-limiting reaction is the dissociation of the enzyme-substrate complex in the microsomal preparations. 4. In the mechanism of action of carbonyl cyanide m-chlorophenylhydrazone the key step may be the electrostatic interaction of its protonated form and one of the forms of activated oxygen at the catalytic centre of cytochrome P-450. 5. at least two different phospholipid-dependent hydrophobic zones are assumed to exist in the microsomal membrane, both coupled with cytochrome P-450. One of them reveals selective sensitivity to the protonation action of carbonyl cyanide m-chlorophenylhydrazone and contains the 'binding protein' for type I substrates and NADPH-cytochrome P-450 reductase; the other contains the cytochrome P-450 haem group and binding sites for type II substrates.
D000632:Aminopyrine / Q000378:metabolism; D000633:Aminopyrine N-Demethylase / Q000037:antagonists & inhibitors; D000814:Aniline Compounds / Q000378:metabolism; D000817:Anilino Naphthalenesulfonates / Q000494:pharmacology; D000818:Animals; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology*; D003486:Cyanides / Q000494:pharmacology; D065607:Cytochrome P-450 Enzyme Inhibitors; D003579:Cytochrome Reductases / Q000378:metabolism; D003840:Deoxycholic Acid / Q000494:pharmacology*; D006420:Hemeproteins / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects* / Q000378:metabolism; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D009570:Nitriles / Q000494:pharmacology*; D011485:Protein Binding / Q000187:drug effects; D051381:Rats
D000814:Aniline Compounds; D000817:Anilino Naphthalenesulfonates; D003486:Cyanides; D065607:Cytochrome P-450 Enzyme Inhibitors; D006420:Hemeproteins; D009570:Nitriles; D003840:Deoxycholic Acid; D000632:Aminopyrine; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D000633:Aminopyrine N-Demethylase; D003579:Cytochrome Reductases; D009251:NADPH-Ferrihemoprotein Reductase