Search

Kinetic models of inactivation of cyclooxygenase and peroxidase activities of prostaglandin-H-synthase (PGHS) during cyclooxygenase and peroxidase reactions catalyzed by the enzyme and also on preincubation with H2O2 have been developed; these models account for data obtained by the authors as well as data from the literature. Being rather simple, these models simultaneously describe the processes of cyclooxygenase and peroxidase inactivation of PGHS, using the minimal set of experimental parameters.

Prostaglandin-H-synthase (PGHS) is a bifunctional enzyme catalyzing cyclooxygenase and peroxidase reactions and undergoing irreversible inactivation during catalysis. A new method for kinetic studies of both PGHS activities in the course of cyclooxygenase as well as peroxidase reactions and also preincubation with hydroperoxides is suggested. It is shown that peroxidase activity is retained after complete cyclooxygenase inactivation and cyclooxygenase activity is retained after complete peroxidase inactivation. Two-stage cyclooxygenase inactivation occurs on preincubation of PGHS with hydrogen peroxide. Studies on inactivation under various conditions indicate that chemical mechanisms of cyclooxygenase and peroxidase inactivation are different. The data allow development of kinetic models.

Prostaglandin-H-synthase (PGHS, EC 1.14.99.1) catalyzes the first committed step in biosynthesis of all prostaglandins, thromboxanes, and prostacyclins by converting arachidonic acid to prostaglandin H(2) (PGH(2)). PGHS exhibits two enzymatic activities: cyclooxygenase activity converting arachidonic acid to prostaglandin G(2) (PGG(2)) and peroxidase activity reducing the hydroperoxide PGG(2) to the corresponding alcohol, PGH(2). Despite the many investigations of the kinetics of PGHS, many features such as the absence of competition and mutual activation between the cyclooxygenase and peroxidase activities cannot be explained in terms of existing schemes. In this work we have studied the influence of different electron donors (N,N,N ,N -tetramethyl-p-phenylenediamine, L-epinephrine, 2,2 -azinobis(3-ethylbenzthiazoline-6-sulfonic acid), potassium ferrocyanide) on the PGHS activities. The proposed scheme describes independent but interconnected cyclooxygenase and peroxidase activities of PGHS. It also explains the experimental data obtained in the present work and known from the literature.