成人做爰免费视频免费看_成人a级高清视频在线观看,成人a大片在线观看,成人a大片高清在线观看,成人av在线播放,一a一级片,一级黄 中国色 片,一级黄 色蝶 片,一级黄色 片生活片

Tubulin is the major constituent of microtubules, a cylinder consisting of laterally associated linear protofilaments composed of alpha- and beta-tubulin heterodimers. Tubulin α- and β-subunits have molecular weights of ~ 50 kDa and are 36%–42% identical and 63% homologous. Both tubulin subunits bind guanine nucleotides. The binding to α-tubulin at the N-site is nonexchangeable, while the binding to β-tubulin at the E-site is exchangeable. Nucleotide in microtubules does not exchange with the solution, except for terminal subunits at microtubule ends.