PROSTAGLANDIN SYNTHETASE - INACTIVATION OF ENDOPEROXIDE-PROSTAGLANDIN SYNTHETASE, A LIMITING ENZYME IN THE SYNTHESIS OF PROSTAGLANDINS

A quantitative approach was utilized to investigate the 1st stage of biospecific synthesis of prostaglandins catalyzed by endoperoxide-prostaglandin synthetase. Integral kinetics of O2 consumption were examined for the arachidonic acid oxidation. The enzyme inactivation in the course of the reaction was studied. Possible mechanisms of inactivation were analyzed: monomolecular inactivation of the enzyme or enzyme-substrate complex, as well as bimolecular inactivation by substrate of product. Analysis of the inactivation kinetic parameters revealed that hemin-catalyzed reaction with O2 contributes mainly to this process. The following parameters were obtained: Km for arachidonic acid, O2 and electron donors; apparent inactivation constant (1.6 .+-. 0.2 min-1). Kd for the apoenzyme-hemin complex and the reaction catalytic constant were also determined.