Roufogalis B D, Mauldin D
Can J Biochem. 1980 Oct;58(10):922-7. doi: 10.1139/o80-126.
The Ca2+ affinity of (Mg2+ + Ca2+)-ATPase in human red blood cells is regulated by a number of intracellular factors, including the association of the enzyme with the cytosolic Ca2+ binding protein, calmodulin. Ghosts prepared by hypotonic lysis in the presence of 0.1 mM CaCl2, or by a gradual stepwise hemolysis procedure, contain an EDTA-extractable protein whose effects are mimicked by calmodulin, whereas ghosts prepared by extensive washes in the absence of added CaCl2 lack calmodulin and contain only a high molecular weight heat stable activator. Purified calmodulin from human red cells or bovine brain shifts the apparent Ca2+ affinity of (Mg2+ + Ca2+)-ATPase activity in extensively washed ghosts to a high Ca2+ affinity state. The shift was most apparent in ghosts in which the Ca2+ affinity was decreased by EDTA treatment. Calmodulin increased the velocity of (Mg2+ + Ca2+)-ATPase in the EDTA-treated ghosts about 36-fold at a low (1.4 microM) Ca2+ concentration, compared with 6-fold before EDTA treatment. The maximum shift in apparent Ca2+ affinity occurred only in the presence of saturating concentrations of calmodulin. It is concluded that red cell calmodulin confers to the Ca2+ transport ATPase the ability to increase its apparent Ca2+ affinity, as well as its maximum velocity, in response to increases in intracellular Ca2+.
人红细胞中（Mg2+ + Ca2+）-ATP酶的Ca2+亲和力受多种细胞内因子调节，包括该酶与胞质Ca2+结合蛋白钙调蛋白的结合。在0.1 mM CaCl2存在下通过低渗裂解制备的血影，或通过逐步溶血程序制备的血影，含有一种可被EDTA提取的蛋白，其作用可被钙调蛋白模拟，而在无添加CaCl2的情况下通过大量洗涤制备的血影则缺乏钙调蛋白，仅含有一种高分子量热稳定激活剂。从人红细胞或牛脑中纯化的钙调蛋白可将大量洗涤后的血影中（Mg2+ + Ca2+）-ATP酶活性的表观Ca2+亲和力转变为高Ca2+亲和力状态。这种转变在经EDTA处理后Ca2+亲和力降低的血影中最为明显。在低（1.4 microM）Ca2+浓度下，钙调蛋白使经EDTA处理的血影中（Mg2+ + Ca2+）-ATP酶的速度增加约36倍，而在EDTA处理前为6倍。表观Ca2+亲和力的最大转变仅在钙调蛋白饱和浓度存在时发生。结论是红细胞钙调蛋白赋予Ca2+转运ATP酶能力，使其在细胞内Ca2+增加时提高其表观Ca2+亲和力及其最大速度。
