Kasson B G, Levin S R
Biochim Biophys Acta. 1981 Nov 13;662(1):30-5. doi: 10.1016/0005-2744(81)90219-9.
Ca2+-dependent ATPase (Ca2+-dependent ATP phosphohydrolase, EC 3.6.1.3) present in a subcellular fraction derived from rat pancreatic islet homogenates was examined to determine kinetic parameters and responses to various substances with known effects upon insulin secretion. Experiments demonstrated the presence of a Ca2+-ATPase with a Km ATP of 7 . 10(-5) M and two Km Ca of 1.3 . 10(-7) M and 5.7 . 10(-6) M. The enzyme had little activity in acidic media while retaining considerable activity in basic media. Optimal activity was obtained at pH 7.5. The enzyme was relatively temperature insensitive (Q10 = 1.49), since activity decreased less than 50% with a 15 degrees C decrease in temperature. Studies on the stability of enzyme activity upon storage at -20 degrees C indicated that for intact islets activity was stable for 3 weeks, while in homogenates activity was stable for only 1 week, after which activity rapidly declined in both cases. Certain substances known to either stimulate or inhibit insulin secretion were tested for their ability to alter enzyme activity. Potassium, glibenclamide and cyclic AMP had no effects upon activity. These observations are consistent with the hypothesis that a Ca2+-ATPase present in pancreatic islets may act as a modulator of pancreatic islet beta cell activity.
对源自大鼠胰岛匀浆的亚细胞组分中存在的钙依赖性ATP酶（钙依赖性ATP磷酸水解酶，EC 3.6.1.3）进行了检测，以确定其动力学参数以及对各种已知对胰岛素分泌有影响的物质的反应。实验证明存在一种钙ATP酶，其ATP的Km为7×10⁻⁵ M，钙的两个Km分别为1.3×10⁻⁷ M和5.7×10⁻⁶ M。该酶在酸性介质中活性很低，而在碱性介质中保持相当高的活性。在pH 7.5时获得最佳活性。该酶对温度相对不敏感（Q10 = 1.49），因为温度降低15℃时活性降低不到50%。对酶活性在-20℃储存时稳定性的研究表明，对于完整胰岛，活性在3周内稳定，而在匀浆中活性仅稳定1周，此后两种情况下活性均迅速下降。测试了某些已知能刺激或抑制胰岛素分泌的物质改变酶活性的能力。钾、格列本脲和环磷酸腺苷对活性无影响。这些观察结果与以下假设一致：胰岛中存在的钙ATP酶可能作为胰岛β细胞活性的调节剂。
