Prishchepa L A, Kondratiuk T P, Kurskiĭ M D
Biokhimiia. 1990 May;55(5):905-10.
Calmodulin activates the ATP-dependent transport of Ca2+. The V0 value for this reaction in the absence of calmodulin is 0.82, that in the presence of 10(-7) M calmodulin is 5 times as high, i. e. 4.5 nmol 45Ca2+/mg protein/min. The Vmax value in the absence of calmodulin is 2.07, that with the activator is 4.33 nmol 45Ca2+/mg protein/min. The corresponding Km values are 0.75 X 10(-6) M and 0.66 X 10(-7) M, respectively, i. e., the affinity of the Ca-pump for Ca2+ increases. The half-maximum Ca-binding activity of calmodulin measured with a help of the fluorescent probe, N-phenyl-1-naphthylamine (PNA), is observed at 5 X 10(-7) M Ca2+. Mg2+ (3 mM) decreases 10-fold the Ca-binding affinity. No significant effect of ATP on the Ca-binding properties of calmodulin was found; the Hill coefficient is suggestive of a positive cooperativity of this reaction. A comparison of dependences of the calmodulin-stimulated component of ATP-dependent transport of Ca2+ in myometrium plasma membranes and of the Ca-binding activity of calmodulin measured with a help of PNA suggests that the effect of calmodulin on the affinity of the Ca-pump for Ca2+ can also be realized when some (but not all) Ca-binding sites in the calmodulin molecule are saturated with Ca2+.
钙调蛋白激活Ca2+的ATP依赖性转运。在没有钙调蛋白的情况下，该反应的V0值为0.82，在存在10^(-7) M钙调蛋白的情况下，该值高5倍，即4.5 nmol 45Ca2+/mg蛋白质/分钟。在没有钙调蛋白的情况下，Vmax值为2.07，有激活剂时为4.33 nmol 45Ca2+/mg蛋白质/分钟。相应的Km值分别为0.75×10^(-6) M和0.66×10^(-7) M，即钙泵对Ca2+的亲和力增加。借助荧光探针N-苯基-1-萘胺（PNA）测得的钙调蛋白的半最大Ca结合活性在5×10^(-7) M Ca2+时观察到。Mg2+（3 mM）使Ca结合亲和力降低10倍。未发现ATP对钙调蛋白的Ca结合特性有显著影响；希尔系数表明该反应具有正协同性。对子宫肌层质膜中Ca2+的ATP依赖性转运的钙调蛋白刺激成分的依赖性与借助PNA测得的钙调蛋白的Ca结合活性的依赖性进行比较表明，当钙调蛋白分子中的一些（但不是全部）Ca结合位点被Ca2+饱和时，钙调蛋白对钙泵与Ca2+亲和力的影响也可以实现。
