Formby B, Capito K, Egeberg J, Hedeskov C J
Am J Physiol. 1976 Feb;230(2):441-8. doi: 10.1152/ajplegacy.1976.230.2.441.
Ca-stimulated ATPase activity has been demonstrated in homogenates of mouse pancreatic islets. On subcellular fractionation Ca-ATPase activity was found in secretory granules, mitochondria, and microsomes, but not in the postmicrosomal fractions. Highest specific activity was found in the granules. In all active subcellular fractions two Km(Ca) values for Ca-ATPase around 7.0 X 10(-6) and 1.8 X 10(-7) M were estimated. Assuming an ATP hydrolysis:Ca pumping ratio of 1:2, the highest capacity for active Ca transport was found in secretory granules and mitochondria. Concentrations of 40 mM or higher of Na and 10(-5) M cyclic AMP inhibited Ca-ATPase in all subfractions. Caffeine at a concentration of 10 mM inhibited Ca-ATPase significantly in secretory granules and microsomes. Also MG-ATPase activity was demonstrated in the various subfractions. This activity was compared with that of Ca-ATPase at identical concentrations of free metal ions and in the absence or presence of various inhibitors. It was concluded that high-affinity Ca-ATPase and Mg-ATPase are two different enzymic entities. Ca-ATPase may tentatively be assumed to participate in active transport of Ca between intracellular compartments and to constitute a Ca-accumulating system which returns the cytosolic free Ca concentration to the resting state after stimulation of the beta-cells by secretagogues. This enzyme may therefore play a significant role in regulation of insulin release.
在小鼠胰岛匀浆中已证实存在钙刺激的ATP酶活性。在亚细胞分级分离时，发现分泌颗粒、线粒体和微粒体中有钙ATP酶活性，但在微粒体后组分中未发现。颗粒中的比活性最高。在所有有活性的亚细胞组分中，估计钙ATP酶的两个Km（Ca）值分别约为7.0×10⁻⁶和1.8×10⁻⁷M。假设ATP水解与钙泵出的比率为1:2，则在分泌颗粒和线粒体中发现了最高的活性钙转运能力。40 mM或更高浓度的钠和10⁻⁵M的环磷酸腺苷抑制了所有亚组分中的钙ATP酶。10 mM浓度的咖啡因显著抑制了分泌颗粒和微粒体中的钙ATP酶。在各种亚组分中也证实了镁ATP酶活性。将该活性与在相同游离金属离子浓度下以及在不存在或存在各种抑制剂的情况下的钙ATP酶活性进行了比较。得出的结论是，高亲和力钙ATP酶和镁ATP酶是两种不同的酶实体。可以初步假定钙ATP酶参与细胞内区室之间钙的主动转运，并构成一个钙积累系统，该系统在促分泌剂刺激β细胞后将细胞质游离钙浓度恢复到静息状态。因此，这种酶可能在胰岛素释放的调节中起重要作用。
