Caplow M, Shanks J
Department of Biochemistry, University of North Carolina, Chapel Hill 27599-7260.
J Biol Chem. 1990 Jan 25;265(3):1414-8.
Dampened oscillations of microtubule assembly can accompany polymerization at high tubulin subunit concentrations. This presumably results from a synchronization of dynamic instability behavior, which generates a large population of rapidly disassembling microtubules, that liberate tubulin-GDP oligomers. Subunits in oligomers cannot assemble until they dissociate, to allow GDP-GTP exchange. To determine whether rapidly disassembling microtubules generate oligomers directly, we measured the rate of dilution-induced disassembly of tubulin-GDP microtubules and the rate of dissociation of GDP from the so-formed tubulin-GDP subunits. The rate of GDP dissociation from liberated subunits was found to correspond to that of tubulin-GDP subunits (t1/2 = 5 s), rather than tubulin-GDP oligomers. This indicates that tubulin-GDP subunits are released from microtubules undergoing rapid disassembly. Oligomers apparently form in a side reaction from the high concentration of tubulin-GDP subunits liberated from the synchronously disassembling microtubule population. The rate of subunit dissociation is 0.11 s-1 with oligomers formed by concentrating tubulin-GDP subunits and 0.045 s-1 with oligomers formed by cold-induced microtubule disassembly. This difference provides evidence that the conformation of tubulin-GDP subunits released from rapidly disassembling microtubules differs from tubulin-GDP subunits that were not recently in the microtubule lattice.
在高微管蛋白亚基浓度下，微管组装的振荡减弱可能伴随聚合过程。这可能是由于动态不稳定性行为的同步化导致的，这种同步化产生了大量迅速解聚的微管，这些微管释放出微管蛋白 - GDP寡聚体。寡聚体中的亚基在解离以允许GDP - GTP交换之前无法组装。为了确定迅速解聚的微管是否直接产生寡聚体，我们测量了微管蛋白 - GDP微管稀释诱导的解聚速率以及GDP从如此形成的微管蛋白 - GDP亚基上解离的速率。发现从释放的亚基上解离的GDP速率与微管蛋白 - GDP亚基的速率相对应（半衰期 = 5秒），而不是微管蛋白 - GDP寡聚体的速率。这表明微管蛋白 - GDP亚基是从经历快速解聚的微管中释放出来的。寡聚体显然是在一个副反应中由从同步解聚的微管群体中释放的高浓度微管蛋白 - GDP亚基形成的。通过浓缩微管蛋白 - GDP亚基形成的寡聚体，亚基解离速率为0.11 s⁻¹，通过冷诱导微管解聚形成的寡聚体，亚基解离速率为0.045 s⁻¹。这种差异提供了证据，表明从迅速解聚的微管中释放的微管蛋白 - GDP亚基的构象与最近不在微管晶格中的微管蛋白 - GDP亚基不同。
