Bayley P M, Martin S R
Biochem Biophys Res Commun. 1986 May 29;137(1):351-8. doi: 10.1016/0006-291x(86)91217-9.
GDP reduces both the rate and amplitude of GTP-induced assembly of microtubules from tubulin dimer or from microtubule protein, and promotes disassembly from microtubules at the steady state. One interpretation postulates that added GDP modifies microtubule ENDS so that tubulin-GTP, the species involved in steady state elongation of microtubules, cannot bind to a microtubule END containing tubulin-GDP. This concept has been used in subsequent models of assembly which treat the 'dynamic instability' of microtubules. We question this interpretation on the basis of the published experimental data and the results reported here. Using a relatively simple model for microtubule assembly, we show by numerical simulation that the quantitative effects of GDP on the rate and amplitude of microtubule assembly and inhibition of steady state GTPase activity are well accounted for by the nucleotide exchange equilibrium of tubulin-GDP and tubulin-GTP. We therefore conclude that the effect of added GDP on elongation of MAP-containing microtubules and on steady state GTPase activity does not indicate modification of the activity of microtubule ENDs but depends on the tubulin-GTP/tubulin-GDP equilibrium. Additional evidence argues that microtubule ENDS containing GDP can indeed accept elongation by tubulin-GTP.
GDP降低了由微管蛋白二聚体或微管蛋白形成的微管在GTP诱导下的组装速率和幅度，并在稳态下促进微管的解聚。一种解释假定，添加的GDP会修饰微管末端，使得参与微管稳态延长的微管蛋白-GTP不能与含有微管蛋白-GDP的微管末端结合。这一概念已被用于后续处理微管“动态不稳定性”的组装模型中。基于已发表的实验数据和此处报道的结果，我们对这一解释提出质疑。通过使用一个相对简单的微管组装模型，我们通过数值模拟表明，GDP对微管组装速率和幅度以及对稳态GTP酶活性的抑制作用的定量效应，可以通过微管蛋白-GDP和微管蛋白-GTP的核苷酸交换平衡得到很好的解释。因此，我们得出结论，添加的GDP对含微管相关蛋白（MAP）的微管延长和稳态GTP酶活性的影响并不表明微管末端活性的改变，而是取决于微管蛋白-GTP/微管蛋白-GDP平衡。其他证据表明，含有GDP的微管末端确实可以接受微管蛋白-GTP的延长。
