跨膜Ca^(2+)梯度对肌质网Ca^3+-ATP酶调节的特异性

THE SPECIFICITY OF MODULATION OF SARCOPLASMIC RETICULUM Ca^(2+)-ATPase BY TRANSMEMBRANE Ca^(2+)GRADIENT

我们曾报道跨膜Ca^(2+)梯度可通过膜脂影响肌质网Ca^(2+)-ATP 酶的构象和活性。本文就跨膜Ca^(2+)梯度对肌质网Ca^(2+)-ATP 酶的调节是否具有特异性作进一步研究。结果表明这种特异性表现在两方面:一是跨膜Ca^(2+)梯度对肌质网Ca^(2+)-ATP 酶功能的调节不能归结于跨膜Ca^(2+)浓度梯度所导致的膜电位的作用,离子载体FCCP 可消除跨膜电位但并不影响肌质网Ca^(2+)-ATP 酶的活力;二是其它二价金属离子如Sr^(2+)的跨膜梯度对肌质网Ca^(2+)-ATP 酶活力基本无影响。荧光偏振系列探剂n-AS 测定的结果表明跨膜Ca^(2+)与Sr^(2+)梯度对嵌有Ca^(2+)-ATP 酶的脂酶体的中部流动性的影响有较大差异。而Ca^(2+)-ATP 酶的Ca^(2+)结合位点正处于脂双层中部,这进一步提示膜脂参与了跨膜Ca^(2+)梯度对Ca^(2+)-ATP 酶的调节作用。

We have previously reported that trans-membrane Ca^(2+)gradient-mediated changesin lipid fluidity could modulate the confo-rmation and enzyme activity of sarcoplas-mic reticulum(SR)Ca^(2+)-ATPase.Theaim of this paper is to explore the speci-ficity of transmembrane Ca^(2+)gradient-me-diated modulation of SR Ca^(2+)-ATPase.Theresults showed that such specificity exhi-bited in two aspects:1.The modulationcould not be ascribed to transmembranepotential resulted from the transmembraneCa^(2+)gradient,Dissipation of transmembranepotential by FCCP(carbonylcyanide-p-tri-fluoromethoxyphenylhydrazone)could notaffect the activity of SR Ca^(2+)-ATPase.2.Transmembrane Sr^(2+)gradient had little ef-fect on the enzyme activity of SR Ca^(2+)-ATPase.A significant difference betweenthe effect of transmembrane Ca^(2+)and Sr^(2+)gradient on the lipid fluidity was detectedin the middle region of bilayer of Ca^(2+)-ATPase incorporated proteoliposomes usinga set of n-AS[n-(9-anthroyloxy)fattyacids]fluorescence polarization probes.Itis known that Ca^(2+)binding domain of SRCa^(2+)-ATPase is just located in the middleregion of bilayer,hence it may be deducedthat possibly,membrane lipids are involvedin transmembrane Ca^(2+)gradient-mediatedmodulation of Ca^(2+)-ATPase.