F. Kurosaki et al., Free coenzyme A-induced activation of a multifunctional polyketide biosynthetic enzyme 6-hydroxymellein synthase in carrot cells, PLANT SCI, 147(2), 1999, pp. 149-155
6-Hydroxymellein (6HM) synthase, a multifunctional polyketide biosynthetic
enzyme in carrot, catalyzes the condensation of acyl-CoAs and the reduction
of the ketomethylene intermediate, and the enzyme activity markedly increa
ses in the presence of submillimolar concentrations of CoA. However, the re
action rate was appreciably decreased by the addition of CoA when the ketor
educing process was omitted from the series of partial reactions of 6HM bio
synthesis. The velocity of the catalytic reaction of the CoA-associated syn
thase showed a marked increase in 6HM formation, while the value of the con
densation reaction did not show the significant change even in the presence
of CoA. The optimal pH of the 6HM synthase-catalyzing reactions shifted fr
om 7.5-8.0 to 6.0 by the addition of CoA only when the ketoreducing reactio
n was involved. These results suggest that the association of free CoA with
6HM synthase protein evokes the alternation of microstructure at the react
ion center of the enzyme, which results in the enhancement of the reaction
rate of ketoreduction involved in 6HM biosynthesis. (C) 1999 Elsevier Scien
ce Ireland Ltd. All rights reserved.