Biochemical properties of the prostaglandin/thromboxane synthetase of human blood platelets and comparison with the synthetase of bovine seminal vesicles.

The enzyme system which synthesizes prostaglandins and thromboxanes in extracts of washed human platelets has been characterized with respect to kinetic parameters, pH and cofactor dependence, and inhibitor potencies. Arachidonate and dihomo-gamma-linolenate were shown to be mutually competitive substrates, thus providing biochemical support for the assumption that both substrates are metabolized by the same cyclooxygenase, although they are ultimately metabolized to different patterns of products. Products of the synthetase of human leucocytes qualitatively resemble those obtained with human platelets. The prostaglandin synthetase of bovine seminal vesicles was studied under similar conditions, and kinetic parameters and inhibitor potencies were compared with those of platelet extracts.