Tsujishita Y, Asaoka Y, Nishizuka Y
Department of Biochemistry, Kobe University School of Medicine, Japan.
Proc Natl Acad Sci U S A. 1994 Jul 5;91(14):6274-8. doi: 10.1073/pnas.91.14.6274.
Permeabilized human leukemia HL-60 and U-937 cells suspended in an acidic or alkaline medium release various unsaturated fatty acids, most abundantly oleic and arachidonic acids. Concomitant production of lysophospholipids suggests that phospholipases A2 play a major role in this fatty acid release reaction. The fatty acid release at acidic conditions depends on the intracellular Ca2+ concentrations at the 10(-8)-10(-7) M range and is enhanced by membrane-permeant diacylglycerols, although this enhancement seems independent of protein kinase C activation. On the other hand, the fatty acid release at alkaline conditions is potentiated by vanadate, and this potentiation is counteracted by genistein, suggesting a role of tyrosine phosphorylation in this release reaction. GTP[gamma S], an activator of G proteins, greatly enhances the fatty acid release. Aluminum fluoride, another activator of heterotrimeric G proteins, also greatly potentiates this release reaction. Phorbol ester increases the fatty acid release at alkaline conditions, to some extent, whereas it counteracts the vanadate-induced potentiation of fatty acid release. The results imply that several phospholipases A2 are coupled to receptors for their activation, thereby functioning in the transmembrane control of cellular events.
悬浮于酸性或碱性介质中的通透化人白血病HL - 60和U - 937细胞会释放各种不饱和脂肪酸，其中油酸和花生四烯酸含量最为丰富。同时产生的溶血磷脂表明磷脂酶A2在这种脂肪酸释放反应中起主要作用。酸性条件下的脂肪酸释放取决于细胞内10(-8)-10(-7)M范围内的Ca2+浓度，且会被膜通透的二酰基甘油增强，尽管这种增强似乎与蛋白激酶C的激活无关。另一方面，碱性条件下的脂肪酸释放会被钒酸盐增强，而这种增强会被染料木黄酮抵消，这表明酪氨酸磷酸化在该释放反应中起作用。G蛋白激活剂GTP[γS]能极大地增强脂肪酸释放。异三聚体G蛋白的另一种激活剂氟化铝也能极大地增强这种释放反应。佛波酯在一定程度上会增加碱性条件下的脂肪酸释放，而它会抵消钒酸盐诱导的脂肪酸释放增强。结果表明，几种磷脂酶A2与受体偶联以实现激活，从而在细胞事件的跨膜调控中发挥作用。
