[Inactivation of prostaglandin endoperoxide synthetase from the microsomal fraction of human platelets during the reaction].

The kinetic regularities of the prostaglandin endoperoxide synthetase in human platelets microsomes were studied. It was shown that at low equilibrium of the reaction the reaction product yield linearly depends on the enzyme concentration. The value of the inactivation rate constant is not dependent on the enzyme concentration, is not changed within the pH range of 6-9 and is markedly increased with a rise in hemin concentration. The kinetics of thermoinactivation of the enzyme at 4 degrees and 32 degrees was studied. It was concluded that inactivation occurs via intermediate enzyme-substrate complexes. The enzyme is also inactivated in the presence of hemin and oxygen. The latter process is eliminated in the presence of an electron donor (epinephrine) in a medium.