抄録
Phospholipase A2 when activated by hormonal stimuli via receptor-mediated process, releases arachidonic acid from membrane phospholipids to produce biologically active eicosanoids. This activity has been known to be modulated by a variety of factors, such as G-protein, protein kinase A and also C, lipocortin, and Na+/H+ exchanger, other than by intracellular Ca2+. However, we here demonstrate in platelet that decrease in lipid phase fluidity of the membranes, induced by cholesterol-enrichment or lipid peroxidation enhances the phospholipase A2 activity, whereas the increase by incorporation of unsaturated fatty acids into the membranes exerts the opposite effect. Consequently, the lipid fluidity appears to affect the receptor-enzyme coupling rather than the enzyme molecule itself, and hence to be implicated in the factors modulating the enzyme activity.
