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 |
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Authors: | J P Salaun D Reichhart A Simon F Durst N O Reich P R Ortiz de Montellano |
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Institution: | Department of Microbiology, University of British Columbia, Vancouver, British Columbia V6T 1W5, Canada |
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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. |
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Keywords: | To whom correspondence should be addressed |
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