抄録
The biosynthesis of phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylserine (PS) by base-exchange reactions, and of PC and PE by the major pathway (ethanolaminephosphotransferase (EPT) and cholinephosphotransferase (CPT) ), was assessed in the membranes of human leukocyte subsets. Among the three base-exchange activities, ethanolamine-exchange was the highest, and choline-exchange the lowest. In major pathway, EPT and CPT had comparable activities. Among leukocyte subpopulations, T lymphocytes showed the highest levels of each enzyme activity, and neutrophils showed the least. Base-exchange activities were increased by addition of Ca++ but inhibited by Mg++ while EPT and CPT were inhibited by Ca++ but enhanced by Mg++. However, each base-exchange was also enhanced by calmodulin inhibitors and inhibited by calmodulin, suggesting that base-exchange reaction is dependent on Ca++ but inhibited by Ca-calmodulin complex. Among the enzyme activities tested, PE formation alone was increased by the presence of low concentrations of bioactive stimulants. Our recent reports showed increased ethanolamine-exchange activity in the patients with various inflammatory disorders. These postulate that although its biological significance is unknown, base-exchange activities may be related to cell activation and that PE formation in base-exchange is a precursor of N-transmethylation of PE, leading to the production of arachidonic acid cascade through PC by phospholipase A2 activity.
