Gordon D J, Yang Y Z, Korn E D
J Biol Chem. 1976 Dec 10;251(23):7474-9.
The kinetics and thermodynamics for the polymerization of purified Acanthamoeba actin were studied and compared to muscle actin. Polymerization was qualitatively similar for the two actins with a rate-limiting nucleation step followed by rapid polymer extension. Polymerization occurred only above a threshold critical concentration which varied with polymerization conditions for each actin. In the presence of 2 mM MgCl2, nucleation of both actins was rapid and their critical concentrations were similarly low and not detectably dependent on temperature. In 0.1 M KCl, the rates of nucleation of both actins were much slower than when Mg2+ was present and were significantly different from each other. Also, under these conditions, the critical concentrations of Acanthamoeba and muscle actin were significantly different and both varied markedly with temperature. These quantitative differences between the two actins could be attributed to differences in both their enthalpies and entropies of polymerization, Acanthamoeba actin having the more positive deltaH and delta S. Co-polymerization of the two actins was also demonstrated. Overall, however, there were no qualitative differences between Acanthamoeba and muscle actin that would suggest a unique role for the monomer-polymer equilibrium of cytoplasmic actin in cell motility.
对纯化的棘阿米巴肌动蛋白聚合反应的动力学和热力学进行了研究，并与肌肉肌动蛋白进行了比较。两种肌动蛋白的聚合反应在性质上相似，都有一个限速成核步骤，随后是快速的聚合物延伸。聚合反应仅在高于阈值临界浓度时发生，该临界浓度随每种肌动蛋白的聚合条件而变化。在2 mM MgCl2存在下，两种肌动蛋白的成核反应都很快，它们的临界浓度同样很低，且未检测到对温度的依赖性。在0.1 M KCl中，两种肌动蛋白的成核速率都比存在Mg2+时慢得多，且彼此有显著差异。此外，在这些条件下，棘阿米巴肌动蛋白和肌肉肌动蛋白的临界浓度有显著差异，且都随温度显著变化。两种肌动蛋白之间的这些定量差异可归因于它们聚合反应的焓和熵的差异，棘阿米巴肌动蛋白具有更正的ΔH和ΔS。还证明了两种肌动蛋白的共聚合。然而，总体而言，棘阿米巴肌动蛋白和肌肉肌动蛋白之间没有质的差异，这表明细胞质肌动蛋白的单体-聚合物平衡在细胞运动中没有独特作用。
