Kim H, Binder L I, Rosenbaum J L
J Cell Biol. 1979 Feb;80(2):266-76. doi: 10.1083/jcb.80.2.266.
Several high molecular weight polypeptides have been shown to quantitatively copurify with brain tubulin during cycles of in vitro assembly-disassembly. These microtubule-associated proteins (MAPs) have been shown to influence the rate and extent of microtubule assembly in vitro. We report here that a heat-stable fraction highly enriched for one of the MAPs, MAP2 (mol wt approximately 300,000 daltons), devoid of MAP1 (mol wt approximately 350,000 daltons), has been purified from calf neurotubules. This MAP2 fraction stoichiometrically promotes microtubule assembly, lowering the critical concentration for tubulin assembly to 0.05 mg/ml. Microtubules saturated with MAP2 contain MAP2 and tubulin in a molar ratio of approximately 1 mole of MAP2 to 9 moles of tubulin dimer. Electron microscopy of thin sections of the MAP2-saturated microtubules fixed in the presence of tannic acid demonstrates a striking axial periodicity of 32 +/- 8 nm.
在体外组装-拆卸循环过程中，已证明有几种高分子量多肽能与脑微管蛋白进行定量共纯化。这些微管相关蛋白（MAPs）已被证明会影响体外微管组装的速率和程度。我们在此报告，已从小牛神经微管中纯化出一种富含MAP2（分子量约为300,000道尔顿）且不含MAP1（分子量约为350,000道尔顿）的热稳定组分。该MAP2组分以化学计量方式促进微管组装，将微管蛋白组装的临界浓度降低至0.05 mg/ml。被MAP2饱和的微管中，MAP2与微管蛋白的摩尔比约为1摩尔MAP2比9摩尔微管蛋白二聚体。在鞣酸存在下固定的MAP2饱和微管薄片的电子显微镜观察显示出32±8 nm的显著轴向周期性。
