Mircevová L, Pick P, Kodícek M, Rehácková H
Biomed Biochim Acta. 1987;46(2-3):S41-5.
The aim of this report was to find which part of the membrane is responsible for the Ca2+ dependence of membrane permeability to K+. We found that the enzyme activity of large contractile complex of membrane proteins, the so called spectrin-dependent ATPase (sp-ATPase) increases at certain Ca2+ concentrations when K+ permeability decreases and vice versa. Ca2+ apparent dissociation constant for sp-ATPase is 6 X 10(-7) M which is the value corresponding to findings of Porzig and Stoffel (1978) for Ca2+ binding to membrane with low K+ permeability. Moreover, 20 chemically quite different substances which inhibit sp-ATPase activity simultaneously increase in the same concentrations K+ permeability and vice versa. No exception was found. The results show that low membrane permeability to K+ occurs at such conformation of sp-ATPase at which its enzyme activity may fully be manifested whereas at other conformations permeability to K+ increases. The conformation of sp-ATPase seems to affect gating mechanism of a respective channel for passive K+ transport through membrane.
本报告的目的是找出细胞膜的哪一部分决定了膜对钾离子通透性的钙离子依赖性。我们发现，膜蛋白的大型收缩复合物（即所谓的血影蛋白依赖性ATP酶，sp-ATP酶）的酶活性在某些钙离子浓度下会随着钾离子通透性的降低而增加，反之亦然。sp-ATP酶的钙离子表观解离常数为6×10⁻⁷ M，这与Porzig和Stoffel（1978年）关于钙离子与低钾离子通透性膜结合的研究结果相符。此外，20种化学性质差异很大的物质在抑制sp-ATP酶活性的同时，会以相同浓度增加钾离子通透性，反之亦然，无一例外。结果表明，当sp-ATP酶处于其酶活性可充分表现的构象时，膜对钾离子的通透性较低，而在其他构象下，对钾离子的通透性会增加。sp-ATP酶的构象似乎影响了钾离子通过膜进行被动转运的相应通道的门控机制。
