Will H, Schirpke B, Wollenberger A
Recent Adv Stud Cardiac Struct Metab. 1976;9:241-8.
Ca2+ binding to a sarcolemma-enriched membrane fraction from pig myocardium possessing an intrinsic cyclic AMP-dependent protein kinase occurs at several classes of low affinity binding sites and at two high affinity binding sites with binding constants of about 1.5-1.7x10(7) M-1 (0.3 nmole of Ca2+/mg protein) and 0.9-2.9x10(6) M-1 (0.8 nmole of Ca2+/mg protein). Ca2+ binding properties are not affected by verapamil and ouabain, whereas ruthenium red depresses Ca2+ binding at the low affinity binding sites and La3+ ions strongly reduce both low and high affinity Ca2+ binding. A profound inhibition of the high affinity Ca2+ binding sites was observed in the presence of Na+ ions, half-maximal inhibition at a free Ca2+ concentration of 2x10(-8) M being achieved by 11 mM NaC1. High affinity Ca2+ binding is also diminished after pretreatment of the membranes with trypsin and phospholipase A. Phosphorylation of one or two of the membrane proteins by the endogenous cyclic AMP-dependent protein kinase leads at both classes of high affinity Ca2+ binding sites to an approximately 4-fold increase in affinity, the number of these sites remaining unchanged. The high affinity Ca2+ binding sites may possibly be involved in Ca2+ extrusion from the cell and in the relaxation process.
钙离子与猪心肌富含肌膜的膜组分结合，该膜组分含有一种内在的环磷酸腺苷依赖性蛋白激酶，结合发生在几类低亲和力结合位点以及两个高亲和力结合位点，其结合常数分别约为1.5 - 1.7×10⁷ M⁻¹（0.3纳摩尔钙离子/毫克蛋白质）和0.9 - 2.9×10⁶ M⁻¹（0.8纳摩尔钙离子/毫克蛋白质）。钙离子的结合特性不受维拉帕米和哇巴因的影响，而钌红会抑制低亲和力结合位点的钙离子结合，镧离子则强烈降低低亲和力和高亲和力的钙离子结合。在钠离子存在的情况下，观察到高亲和力钙离子结合位点受到显著抑制，在游离钙离子浓度为2×10⁻⁸ M时，11 mM氯化钠可实现半数最大抑制。用胰蛋白酶和磷脂酶A预处理膜后，高亲和力钙离子结合也会减少。内源性环磷酸腺苷依赖性蛋白激酶对一种或两种膜蛋白的磷酸化作用，会使两类高亲和力钙离子结合位点的亲和力增加约4倍，而这些位点的数量保持不变。高亲和力钙离子结合位点可能参与细胞内钙离子的排出以及舒张过程。
