title: Inactivation of rat testicular NADPH-cytochrome P-450 reductase by 2,4,6-trinitrobenzenesulfonate.
abstract: Rat testicular NADPH-cytochrome P-450 reductase was inactivated by treatment with 2,4,6-trinitrobenzene sulfonate (TNBS) or with 2',3'-dialdehyde derivatives of 5'-ATP and NADP+. The inactivation rates were dependent on reaction time and followed pseudo-first order kinetics. The rate of inactivation of cytochrome c reducing activity by TNBS was faster than that of reducing activities for K3Fe(CN)6 and for dichlorophenol indophenol (DCPIP). Cytochrome c and DCPIP prevented NADPH-cytochrome P-450 reductase from inactivation by TNBS, but NADP(H) protected to a lesser extent. Stoichiometry indicated that two residues of amino acid modified with TNBS were essential for the enzyme activity. The 2',3'-dialdehyde derivatives of 5'-ATP and NADP+ were specific ligands for the modification of lysine residues, whereas TNBS would possibly modify residues of lysine and/or cysteine. By differential and sequential modification by 5,5'-dithio-bis(2-nitrobenzoic acid), TNBS and dithiothreitol, the residues of lysine and cysteine were identified in the active site of NADPH-cytochrome P-450 reductase. These results suggest that lysyl and cysteinyl residues are located at or near the active region of NADPH-cytochrome P-450 reductase from the rat testicular microsomal fraction.
mesh_terms: D000818:Animals; D007700:Kinetics; D008297:Male; D008861:Microsomes / Q000201:enzymology*; D008970:Molecular Weight; D009251:NADPH-Ferrihemoprotein Reductase / Q000037:antagonists & inhibitors*; D009578:Nitrobenzenes / Q000494:pharmacology*; D051381:Rats; D013737:Testis / Q000201:enzymology*; D014302:Trinitrobenzenesulfonic Acid / Q000494:pharmacology*
chemical_list: D009578:Nitrobenzenes; D014302:Trinitrobenzenesulfonic Acid; D009251:NADPH-Ferrihemoprotein Reductase