Rouayrenc J F, Travers F
Eur J Biochem. 1981 May;116(1):73-7. doi: 10.1111/j.1432-1033.1981.tb05302.x.
In the presence of certain cations (e.g. K+ or Mg2+) actin polymerizes. Below a certain concentration (the critical concentration) the monomer G-actin does not polymerize on the addition of K+ or Mg2+. However, the proteolysis experiments of Rich and Estes [J. Mol. Biol. 104, 777--792 (1976)] strongly suggest that cations induce a change in conformation of G-actin leading to a novel form of actin, G*-actin. This conformational change may be the first step in the polymerization of actin. We have studied G*-actin induced by K+, by difference spectroscopy. We show that G*-actin is a monomer and we confirm that the bound ATP is not cleaved. We also studied the G-actin in equilibrium with G*-actin equilibrium at 4 degrees C as a function of K+ or Mg2+ concentration. With KCl, the transformation can be accounted for as a screening effect. The effect of Mg2+ is more specific and the change in conformation of the G-actin could result from the binding of two or three Mg2+ ions/molecule. We suggest that the G-actin in equilibrium with G*-actin transformation results from the neutralization of a polyanionic region on the actin surface and that this region could be the highly negatively charged N terminus.
在某些阳离子（如K⁺或Mg²⁺）存在的情况下，肌动蛋白会发生聚合。在低于一定浓度（临界浓度）时，添加K⁺或Mg²⁺后单体G - 肌动蛋白不会聚合。然而，Rich和Estes的蛋白水解实验[《分子生物学杂志》104, 777 - 792 (1976)]有力地表明，阳离子会诱导G - 肌动蛋白的构象发生变化，从而产生一种新型的肌动蛋白，即G* - 肌动蛋白。这种构象变化可能是肌动蛋白聚合的第一步。我们通过差示光谱法研究了由K⁺诱导产生的G* - 肌动蛋白。我们发现G* - 肌动蛋白是一种单体，并且证实结合的ATP不会被裂解。我们还研究了在4℃下与G* - 肌动蛋白处于平衡状态的G - 肌动蛋白，其作为K⁺或Mg²⁺浓度的函数。对于KCl，这种转变可以解释为一种屏蔽效应。Mg²⁺的作用更具特异性，G - 肌动蛋白的构象变化可能是由于每分子结合了两个或三个Mg²⁺离子所致。我们认为，与G* - 肌动蛋白处于平衡状态的G - 肌动蛋白转变是由于肌动蛋白表面一个多阴离子区域的中和作用引起的，并且这个区域可能是高度带负电荷 的N末端。
