Owen A, Sener A, Malaisse W J
Enzyme. 1983;29(1):2-14. doi: 10.1159/000469598.
Pancreatic islets can be viewed as a fuel-sensor organ. The amount of ATP used by the islet cells for the maintenance of adequate Ca2+ gradients across membranes is not known. An indirect approach to this issue consists in the measurement of Ca-ATPase activity. The kinetics of Ca-ATPase in islet homogenates yielded a Km for ATP close to 0.1 mM and two Km values for Ca2+ close to 0.13 and 4-6 microM, respectively. Within limits, the Ca-ATPase appeared as a distinct entity from Mg-ATPase. Several divalent cations, including Mg2+, inhibited the Ca-ATPase activity. Calmodulin also inhibited, significantly albeit modestly Ca-ATPase. The activity of the enzyme was increased at high pH or in the presence of bicarbonate. The reaction velocity at close-to-physiological concentrations of ATP, Ca2+ and H+ suggests that the consumption of ATP by the Ca-ATPase may account for a major fraction of the overall rate of ATP breakdown in intact islets.
胰岛可被视为一种燃料传感器官。目前尚不清楚胰岛细胞为维持跨膜的适当钙离子梯度所消耗的三磷酸腺苷（ATP）量。解决这个问题的一种间接方法是测量钙 - 三磷酸腺苷酶（Ca - ATPase）活性。胰岛匀浆中Ca - ATPase的动力学表明，ATP的米氏常数（Km）接近0.1毫摩尔，钙离子的两个Km值分别接近0.13和4 - 6微摩尔。在一定范围内，Ca - ATPase表现为与镁 - 三磷酸腺苷酶（Mg - ATPase）不同的实体。包括镁离子在内的几种二价阳离子抑制Ca - ATPase活性。钙调蛋白也抑制Ca - ATPase，尽管抑制作用较小但具有显著性。在高pH值或存在碳酸氢盐的情况下，该酶的活性会增加。在接近生理浓度的ATP、钙离子和氢离子条件下的反应速度表明，Ca - ATPase对ATP的消耗可能占完整胰岛中ATP分解总速率的很大一部分。
