Pollard T D
J Cell Biol. 1984 Sep;99(3):769-77. doi: 10.1083/jcb.99.3.769.
Using hexokinase, glucose, and ATP to vary reversibly the concentrations of ADP and ATP in solution and bound to Acanthamoeba actin, I measured the relative critical concentrations and elongation rate constants for ATP-actin and ADP-actin in 50 mM KCl, 1 mM MgCl2, 1 mM EGTA, 0.1 mM nucleotide, 0.1 mM CaCl2, 10 mM imidazole, pH 7. By both steady-state and elongation rate methods, the critical concentrations are 0.1 microM for ATP-actin and 5 microM for ADP-actin. Consequently, a 5 microM solution of actin can be polymerized, depolymerized, and repolymerized by simply cycling from ATP to ADP and back to ATP. The critical concentrations differ, because the association rate constant is 10 times higher and the dissociation rate constant is five times lower for ATP-actin than ADP-actin. These results show that ATP-actin occupies both ends of actin filaments growing in ATP. The bound ATP must be split on internal subunits and the number of terminal subunits with bound ATP probably depends on the rate of growth.
我使用己糖激酶、葡萄糖和三磷酸腺苷（ATP）可逆地改变溶液中以及与棘阿米巴肌动蛋白结合的二磷酸腺苷（ADP）和ATP的浓度，测定了在50 mM氯化钾、1 mM氯化镁、1 mM乙二醇双四乙酸（EGTA）、0.1 mM核苷酸、0.1 mM氯化钙、10 mM咪唑、pH值为7的条件下，ATP - 肌动蛋白和ADP - 肌动蛋白的相对临界浓度和伸长速率常数。通过稳态法和伸长速率法，ATP - 肌动蛋白的临界浓度为0.1微摩尔，ADP - 肌动蛋白的临界浓度为5微摩尔。因此，通过简单地从ATP循环到ADP再回到ATP，5微摩尔的肌动蛋白溶液可以进行聚合、解聚和再聚合。临界浓度不同，因为ATP - 肌动蛋白的缔合速率常数比ADP - 肌动蛋白高10倍，解离速率常数比ADP - 肌动蛋白低5倍。这些结果表明，ATP - 肌动蛋白占据了在ATP中生长的肌动蛋白丝的两端。结合的ATP必须在内部分子亚基上被分解，结合ATP的末端分子亚基数量可能取决于生长速率。
