Localization of cyclo-oxygenase and thromboxane synthetase in human platelet intracellular membranes

Abstract
Platelet mixed membrane fractions were separated into discrete vesicle subpopulations of surface and intracellular origin. Intracellular membrane vesicles are the predominant site of phospholipid-modifying enzymes that liberate arachidonic acid. The selective enrichment in intracellular membranes of cyclooxygenase and thromboxane synthetase activities is reported. Surface membrane fractions show no such enrichment. A sequence of activities leading to the biosynthesis of thromboxane from arachidonate is evidently associated with the intracellular membrane elements known as dense tubular membranes.