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

Add time:08/06/2019    Source:sciencedirect.com

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 inchain hydroxylase, but inactivates the enzyme in a time-dependent, pseudo-first-order process with a rate constant of approximately 1.1 × 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 μM). 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.

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