title: Autocatalytic inactivation of plant cytochrome P-450 enzymes: selective inactivation of the lauric acid in-chain hydroxylase from Helianthus tuberosus L. by unsaturated substrate analogs.
abstract: Lauric acid in-chain hydroxylation is inhibited in microsomes from Jerusalem artichoke tubers (Helianthus tuberosus L.) incubated with 9-decenoic, 11-dodecenoic, or 11-dodecynoic acids. 9-Decenoic acid is at best a weak competitive inhibitor of the in-chain hydroxylase, but inactivates the enzyme in a time-dependent, pseudo-first-order process with a rate constant of approximately 1.1 X 10(-3) s-1. In contrast, 11-dodecenoic acid causes a slower, time-dependent loss of the hydroxylase activity, but is a potent competitive inhibitor of the enzyme (Ki = 2 microM). Neither agent decreases the microsomal concentration of cytochrome b5, NADH-cytochrome b5 reductase, or NADPH cytochrome P-450 reductase. Cinnamic acid 4-hydroxylation, catalyzed by a cytochrome P-450 enzyme, is not affected by concentrations of 9-decenoic acid that suppress lauric acid hydroxylation. 11-Dodecenoic acid is much less specific and, at higher concentrations, markedly reduces the microsomal cytochrome P-450 content, and the hydroxylation of both lauric and cinnamic acids.
mesh_terms: D001667:Binding, Competitive; D002384:Catalysis; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System; D006368:Helianthus / Q000201:enzymology; D007700:Kinetics; D007850:Lauric Acids / Q000494:pharmacology*; D008861:Microsomes / Q000201:enzymology; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors*; D009249:NADP / Q000378:metabolism; D010944:Plants / Q000201:enzymology*; D013379:Substrate Specificity
chemical_list: D065607:Cytochrome P-450 Enzyme Inhibitors; D007850:Lauric Acids; C030358:lauric acid; D009249:NADP; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; C032968:lauric acid in-chain-hydroxylase