Angélica Carrasco M, Sierralta J, Hidalgo C
Departamento de Fisiología y Biofísica, Facultad de Medicina, Universidad de Chile, Santiago.
Biochim Biophys Acta. 1993 Oct 10;1152(1):44-8. doi: 10.1016/0005-2736(93)90229-s.
Highly purified triads and transverse tubules, as well as soluble fraction isolated from frog skeletal muscle, hydrolyze exogenous phosphatidylinositol 4,5-bisphosphate forming inositol 1,4,5-trisphosphate with maximal rates in the range 0.5-1 nmol/mg per min at pCa 3. Sarcoplasmic reticulum membranes present a minor activity. The hydrolysis rates in triads were 0.072 +/- 0.015 nmol/mg per min at pCa 7, increasing to 0.263 +/- 0.026 nmol/mg per min at pCa 5 with 1.0 mM Mg and 0.1 mM substrate. The phospholipase C activity of isolated transverse tubules at pCa 3 was 0.570 +/- 0.032 nmol/mg per min. Since triads contain 10% transverse tubules, and correcting for the small contribution of sarcoplasmic reticulum, the calculated phospholipase C activity of transverse tubules at pCa 3 is about 10-times higher than the observed values, suggesting loss of activity during isolation. The activation by calcium was also observed in a soluble fraction and was neither replaced nor inhibited by magnesium. No effect of GTP analogs on phospholipase C activity was detected.
高度纯化的三联体和横小管，以及从青蛙骨骼肌分离得到的可溶性组分，可水解外源性磷脂酰肌醇4,5 - 二磷酸，形成肌醇1,4,5 - 三磷酸，在pCa 3时最大速率在0.5 - 1 nmol/mg每分钟范围内。肌浆网膜呈现出较低的活性。在pCa 7时，三联体中的水解速率为0.072±0.015 nmol/mg每分钟，在pCa 5时，加入1.0 mM镁和0.1 mM底物后，水解速率增加到0.263±0.026 nmol/mg每分钟。分离出的横小管在pCa 3时的磷脂酶C活性为0.570±0.032 nmol/mg每分钟。由于三联体含有10%的横小管，并校正肌浆网的微小贡献后，计算得出横小管在pCa 3时的磷脂酶C活性比观察值高约10倍，这表明在分离过程中活性有所损失。在可溶性组分中也观察到了钙的激活作用，且这种激活作用既不能被镁替代也不受其抑制。未检测到GTP类似物对磷脂酶C活性有影响。
