Tobacman L S, Brenner S L, Korn E D
J Biol Chem. 1983 Jul 25;258(14):8806-12.
The interaction of Acanthamoeba actin and Acanthamoeba profilin was evaluated as a function of ionic conditions. In the presence of 2 mM MgCl2 or 1 mM MgCl2 and 50 mM KCl, profilin decreased the concentration of F-actin at steady state, and inhibited the rates of filament elongation and spontaneous nucleation and polymerization. All of the experimental data were quantitatively accounted for on the basis of a 1:1 complex between profilin and monomeric actin with a Kr between 4 and 9 microM, the same value obtained previously in the absence of MgCl2. Therefore, the Mg2+ concentration did not affect the KD of the profilin-actin complex in these experiments. On the other hand, profilin did greatly amplify the decrease in concentration of F-actin at steady state caused by lowering the Mg2+ concentration. This results from the effect of Mg2+ on the critical concentration of the actin monomer with which the profilin-actin complex is in equilibrium. When the Mg2+ concentration is lowered, the critical concentration of actin monomer increases so that more profilin-actin complex is formed. Thus, appreciably more F-actin depolymerizes than in the absence of profilin. In this way, profilin could function intracellularly to convert small changes in critical concentration into large changes in the concentration of F-actin.
作为离子条件的函数，对棘阿米巴肌动蛋白和棘阿米巴肌动蛋白单体结合蛋白的相互作用进行了评估。在存在2 mM MgCl2或1 mM MgCl2和50 mM KCl的情况下，肌动蛋白单体结合蛋白降低了稳态下F-肌动蛋白的浓度，并抑制了丝状体伸长、自发成核和聚合的速率。所有实验数据均基于肌动蛋白单体结合蛋白与单体肌动蛋白之间1:1的复合物进行定量分析，解离常数（Kr）在4至9 microM之间，这与之前在不存在MgCl2的情况下获得的值相同。因此，在这些实验中，Mg2+浓度并未影响肌动蛋白单体结合蛋白-肌动蛋白复合物的解离常数（KD）。另一方面，肌动蛋白单体结合蛋白确实极大地放大了因降低Mg2+浓度而导致的稳态下F-肌动蛋白浓度的降低。这是由于Mg2+对与肌动蛋白单体结合蛋白-肌动蛋白复合物处于平衡状态的肌动蛋白单体临界浓度的影响。当Mg2+浓度降低时，肌动蛋白单体的临界浓度增加，从而形成更多的肌动蛋白单体结合蛋白-肌动蛋白复合物。因此，与不存在肌动蛋白单体结合蛋白的情况相比，明显更多的F-肌动蛋白发生解聚。通过这种方式，肌动蛋白单体结合蛋白可以在细胞内发挥作用，将临界浓度的微小变化转化为F-肌动蛋白浓度的大幅变化。
