跨膜Ca~(2+)梯度对肌质网Ca~3+-ATP酶调节的特异性

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。

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

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.