Hesketh J E
Int J Biochem. 1984;16(12):1331-9. doi: 10.1016/0020-711x(84)90236-2.
Microtubule assembly has been studied turbidometrically in supernatant fluids prepared from rat brain by high-speed centrifugation. It was confirmed that assembly occurred in the absence of added GTP. Zinc ions (500 microM, but in the presence of 1 mM EGTA) stimulated assembly under these conditions. Zinc-stimulated assembly produced microtubules with normal characteristics, as judged by electron microscopy, SDS-polyacrylamide gel electrophoresis and inhibition of assembly by fructose-6-phosphate or colchicine. However, microtubules formed in the presence of such zinc concentrations were more stable to cold than controls, although the rate constant for the disassembly reaction was unchanged. Neither the stimulation of assembly by zinc nor the effect on cold stability was affected by trifluoperazine suggesting that a calmodulin-related mechanism is not involved. Microtubule "seeds" had little effect in the presence of zinc, suggesting that it may be acting on the nucleation phase of the assembly reaction. This was supported by the findings that zinc reduced the critical concentration of brain supernatant necessary for assembly and that zinc did not affect the rate constant for assembly. The results suggest zinc can in some way stabilize microtubules; possible mechanisms are discussed.
通过高速离心从大鼠大脑制备的上清液中，已采用比浊法研究了微管组装。证实了在未添加鸟苷三磷酸（GTP）的情况下组装也会发生。在这些条件下，锌离子（500微摩尔，但存在1毫摩尔乙二醇双四乙酸（EGTA））刺激了组装。通过电子显微镜、十二烷基硫酸钠-聚丙烯酰胺凝胶电泳以及6-磷酸果糖或秋水仙碱对组装的抑制作用判断，锌刺激的组装产生了具有正常特征的微管。然而，在这种锌浓度下形成的微管比对照对低温更稳定，尽管拆解反应的速率常数没有变化。锌对组装的刺激作用以及对低温稳定性的影响均不受三氟拉嗪的影响，这表明不涉及与钙调蛋白相关的机制。在有锌的情况下，微管“种子”作用很小，这表明锌可能作用于组装反应的成核阶段。锌降低了组装所需的大脑上清液的临界浓度以及锌不影响组装的速率常数这一发现支持了这一点。结果表明锌可以以某种方式稳定微管；讨论了可能的机制。
