Autocatalytic inactivation of plant cytochrome P-450 enzymes: Selective inactivation of cinnamic acid 4-hydroxylase from Helianthus tuberosus by 1-aminobenzotriazole

Abstract

Incubation of either microsomes or slices of Helianthus tuberosus (Jerusalem artichoke) with 1-aminobenzotriazole results in time-dependent autocatalytic inactivation of cinnamic acid 4-hydroxylase, a cytochrome P-450 monooxygenase found only in plants. The inactivation is characterized by a pseudo-first-order rate constant between 4.3 and 16.5 × 10 −3 s −1. Cytochrome b 5 and NADPH cytochrome c ( P-450) reductase are not affected. Lauric acid hydroxylation, a second type of cytochrome P-450 catalyzed reaction, is only weakly inhibited in microsomal incubations. Both lauric acid hydroxylation and cytochrome P-450 levels are decreased in tuber slices by 1-aminobenzotriazole, but at a much slower rate than cinnamic acid hydroxylation. The results suggest that 1-aminobenzotriazole is a selective (perhaps specific) suicide substrate for cinnamic acid 4-hydroxylase in this plant tissue.