Grazi E
Biochem J. 1984 Nov 1;223(3):571-6. doi: 10.1042/bj2230571.
Mg2+, at submicromolar concentrations, is needed for the nucleation of actin [Maruyama (1981) J. Biol. Chem. 256, 1060-1062]. I show here that Mn2+ fulfils the same function. It binds to oligomers present in the ATP-G-actin solutions with a ratio of 2-3 Mn2+ ions per 100 actin monomers and with an association constant of 0.66 X 10(10) M-1 at pH 8.2 at 25 degrees C. The time course of the binding of Mn2+ to polymerizing actin is not affected by the initial concentration of the protein. Analysis of the distribution of the binding shows that, both in the large oligomeric species and in the polymers, 1 Mn2+ ion is bound for every 14-25 actin monomers, whereas in the smaller oligomeric species 1 Mn2+ ion is bound for every 4 actin monomers. The proposal is made that Mn2+ stabilizes actin nuclei and decreases the concentration of the monomers at the steady state. It is also proposed that, at least in some experimental conditions, the direct condensation of oligomers of intermediate length is an effective mechanism of F-actin formation.
亚微摩尔浓度的Mg2+是肌动蛋白成核所必需的[丸山（1981年）《生物化学杂志》256卷，第1060 - 1062页]。我在此表明Mn2+也具有相同功能。它以每100个肌动蛋白单体结合2 - 3个Mn2+离子的比例与ATP - G - 肌动蛋白溶液中的寡聚体结合，在25℃、pH 8.2条件下的缔合常数为0.66×10(10) M-1。Mn2+与正在聚合的肌动蛋白结合的时间进程不受蛋白质初始浓度的影响。对结合分布的分析表明，在大的寡聚体和聚合物中，每14 - 25个肌动蛋白单体结合1个Mn2+离子，而在较小的寡聚体中，每4个肌动蛋白单体结合1个Mn2+离子。有人提出Mn2+能稳定肌动蛋白核并降低稳态下单体的浓度。还提出，至少在某些实验条件下，中等长度寡聚体的直接缩合是F - 肌动蛋白形成的一种有效机制。
