Job D, Fischer E H, Margolis R L
Proc Natl Acad Sci U S A. 1981 Aug;78(8):4679-82. doi: 10.1073/pnas.78.8.4679.
Purified cold-stable microtubules from the rat brain are insensitive to podophyllotoxin and to millimolar concentrations of free calcium. However, in the presence of calmodulin at concentrations substoichiometric to that of tubulin, calcium causes rapid microtubule disassembly. The half-maximal effective calcium concentration in the presence of calmodulin is 100 microM. With 800 microM free calcium, the half-maximal effective concentration of calmodulin is 1.0 microM (or one-tenth the tubulin concentration). Calmodulin is without effect in the absence of calcium. Troponin C is approximately one-fifth as effective as calmodulin, and parvalbumin is totally ineffective. Troponin I partially inhibits the calcium/calmodulin-induced disassembly of microtubules in the crude extract and blocks the calcium/calmodulin effect on purified cold-stable microtubules. A 5-fold excess of trifluoperazine does not inhibit the calcium/calmodulin-induced disassembly.
从大鼠脑中纯化得到的冷稳定微管对鬼臼毒素和毫摩尔浓度的游离钙不敏感。然而，当钙调蛋白的浓度低于微管蛋白的化学计量浓度时，钙会导致微管迅速解体。在钙调蛋白存在的情况下，半数最大效应钙浓度为100微摩尔。当游离钙浓度为800微摩尔时，钙调蛋白的半数最大效应浓度为1.0微摩尔（或微管蛋白浓度的十分之一）。在没有钙的情况下，钙调蛋白没有作用。肌钙蛋白C的效力约为钙调蛋白的五分之一，而小白蛋白则完全无效。肌钙蛋白I部分抑制粗提物中钙/钙调蛋白诱导的微管解体，并阻断钙/钙调蛋白对纯化的冷稳定微管的作用。5倍过量的三氟拉嗪不会抑制钙/钙调蛋白诱导的解体。
