Fatty Acid Cyclooxygenase Induction and Prostaglandin D Synthesis in a Human Megakaryoblastic Cell Line CMK Differentiated by Phorbol Ester

The biosynthesis of prostaglandin (PG) and thromboxane (TX) is initiated by a bifunctional enzyme with oxygenase and peroxidase activities, and PGH2 is produced from arachidonic acid via PGG21. This bifunctional enzyme (prostaglandin endoperoxide synthase, E.C. 1.14.99.1) will be referred to briefly as cyclooxygenase in this chapter. There are two cyclooxygenase isozymes (COX-1 and COX-2), and COX-1 is generally known to be present in human platelets and involved in the synthesis of proaggregatory and vasoconstrictive TXA2. Since platelets have no nucleus and can not synthesize mRNA, the COX-1 protein is derived presumably from megakaryocytes which are precursor cells of platelets.