Selden L A, Gershman L C, Estes J E
J Muscle Res Cell Motil. 1986 Jun;7(3):215-24. doi: 10.1007/BF01753554.
The kinetics of the elongation reaction in the polymerization of actin containing tightly-bound Mg2+ (Mg-actin) or tightly-bound Ca2+ (Ca-actin) have been studied. The reaction was monitored using the increase in fluorescence intensity of N-(1-pyrenyl)iodoacetamide-labelled monomeric actin as a measure of polymer formation. The actin nucleation reaction was circumvented by the addition of phalloidin-stabilized actin nuclei. Elongation rates were obtained at various actin concentrations and at various temperatures for polymerization induced by the presence of different monovalent and divalent salt concentrations. Values for the relative rate constant of forward polymerization (mk+) for Mg-actin were found to be larger than those for Ca-actin under similar conditions (m = number of polymer ends). The critical actin concentration (Cc) of Mg-actin is lower than the Cc for Ca-actin, as were estimates of the relative rate constant of depolymerization (mk-). The temperature dependence of Cc, mk+ and mk- for Mg-actin was different from that for Ca-actin, further suggesting a difference in monomeric properties due to the type of divalent cation tightly bound to actin. Estimates of the activation enthalpy change for the forward reaction in the G in equilibrium F transformation were similar for both types of actin, but the activation enthalpy change for the depolymerization of Mg-actin was significantly larger than that for Ca-actin.
对含有紧密结合的Mg2+（Mg-肌动蛋白）或紧密结合的Ca2+（Ca-肌动蛋白）的肌动蛋白聚合过程中延伸反应的动力学进行了研究。通过监测N-(1-芘基)碘乙酰胺标记的单体肌动蛋白荧光强度的增加来监测反应，以此作为聚合物形成的指标。通过添加鬼笔环肽稳定的肌动蛋白核来规避肌动蛋白成核反应。在不同的肌动蛋白浓度、不同温度下，以及在不同单价和二价盐浓度存在下诱导聚合反应时，获得了延伸速率。发现在相似条件下，Mg-肌动蛋白正向聚合的相对速率常数（mk+）的值大于Ca-肌动蛋白的（m =聚合物末端数量）。Mg-肌动蛋白的临界肌动蛋白浓度（Cc）低于Ca-肌动蛋白的Cc，解聚的相对速率常数（mk-）的估计值也是如此。Mg-肌动蛋白的Cc、mk+和mk-的温度依赖性与Ca-肌动蛋白不同，这进一步表明由于紧密结合到肌动蛋白上的二价阳离子类型不同，单体性质存在差异。两种类型的肌动蛋白在G转变为F平衡时正向反应的活化焓变估计值相似，但Mg-肌动蛋白解聚的活化焓变明显大于Ca-肌动蛋白的。
