Saido T C, Shibata M, Takenawa T, Murofushi H, Suzuki K
Department of Molecular Biology, Tokyo Metropolitan Institute of Medical Science, Japan.
J Biol Chem. 1992 Dec 5;267(34):24585-90.
Whether calcium is the only major intracellular activator of calpain has not yet been established. Here we demonstrate that polyphosphoinositides may play critical roles in the activation process of mu-calpain. Experiments with purified enzyme, substrate (fodrin), and phospholipids show that only polyphosphoinositides but not other lipids significantly promote calpain action in the physiological intracellular calcium range of 10(-7) to 10(-6) M. The effect of polyphosphoinositide is exerted through both a reduction in the calcium concentration required for calpain autolysis and an increase in the Vmax of the proteolytic reaction. Neomycin, a polyphosphoinositide-binding antibiotic, inhibits both polyphosphoinositide-assisted proteolysis in test tubes and calcium-induced calpain activation coupled with substrate proteolysis in intact cells. This implies that the presence of polyphosphoinositides may actually be a prerequisite for calpain activation inside cells.
钙是否是钙蛋白酶唯一主要的细胞内激活剂尚未确定。在此我们证明多磷酸肌醇可能在微钙蛋白酶的激活过程中发挥关键作用。使用纯化的酶、底物（血影蛋白）和磷脂进行的实验表明，在生理细胞内钙浓度范围为10^(-7)至10^(-6)M时，只有多磷酸肌醇而非其他脂质能显著促进钙蛋白酶的作用。多磷酸肌醇的作用是通过降低钙蛋白酶自溶所需的钙浓度以及提高蛋白水解反应的Vmax来实现的。新霉素是一种结合多磷酸肌醇的抗生素，它既抑制试管中多磷酸肌醇辅助的蛋白水解，也抑制完整细胞中钙诱导的钙蛋白酶激活以及底物蛋白水解。这意味着多磷酸肌醇的存在实际上可能是细胞内钙蛋白酶激活的先决条件。
