Korn E D, Carlier M F, Pantaloni D
Laboratory of Cell Biology, National Heart, Lung, and Blood Institute, Bethesda, MD 20892.
Science. 1987 Oct 30;238(4827):638-44. doi: 10.1126/science.3672117.
F-actin is the major component of muscle thin filaments and, more generally, of the microfilaments of the dynamic, multifunctional cytoskeletal systems of nonmuscle eukaryotic cells. Polymeric F-actin is formed by reversible noncovalent self-association of monomeric G-actin. To understand the dynamics of microfilament systems in cells, the dynamics of polymerization of pure actin must be understood. The following model has emerged from recent work. During the polymerization process, adenosine 5'-triphosphate (ATP) that is bound to G-actin is hydrolyzed to adenosine 5'-diphosphate (ADP) that is bound to F-actin. The hydrolysis reaction occurs on the F-actin subsequent to the polymerization reaction in two steps: cleavage of ATP followed by the slower release of inorganic phosphate (Pi). As a result, at high rates of filament growth a transient cap of ATP-actin subunits exists at the ends of elongating filaments, and at steady state a stabilizing cap of ADP.Pi-actin subunits exists at the barbed ends of filaments. Cleavage of ATP results in a highly stable filament with bound ADP.Pi, and release of Pi destabilizes the filament. Thus these two steps of the hydrolytic reaction provide potential mechanisms for regulating the monomer-polymer transition.
F-肌动蛋白是肌肉细肌丝的主要成分，更普遍地说，是非肌肉真核细胞动态多功能细胞骨架系统微丝的主要成分。聚合型F-肌动蛋白由单体G-肌动蛋白通过可逆的非共价自缔合形成。为了解细胞中微丝系统的动力学，必须先了解纯肌动蛋白的聚合动力学。近期研究得出了以下模型。在聚合过程中，与G-肌动蛋白结合的三磷酸腺苷（ATP）水解为与F-肌动蛋白结合的二磷酸腺苷（ADP）。水解反应在聚合反应之后分两步在F-肌动蛋白上发生：ATP裂解，随后是较慢的无机磷酸（Pi）释放。因此，在细丝快速生长时，伸长细丝末端存在由ATP-肌动蛋白亚基构成的瞬时帽，而在稳态时，细丝的倒刺末端存在由ADP·Pi-肌动蛋白亚基构成的稳定帽。ATP裂解产生具有结合ADP·Pi的高度稳定细丝，Pi的释放使细丝不稳定。因此，水解反应的这两个步骤为调节单体-聚合物转变提供了潜在机制。
