Flanagan M D, Lin S
J Biol Chem. 1980 Feb 10;255(3):835-8.
We have found that addition of a small amount of filamentous muscle actin (F-actin) to a solution of globular actin (G-actin) in a low ionic strength medium resulted in rapid polymerization of the G-actin. This reaction was inhibited by substoichiometric levels of cytochalasins (relative potency: cytochalasin D greater than cytochalasin E approximately equal to cytochalasin B greater than dihydrocytochalasin B). Binding experiments show that F-actin, but not G-actin, contains high affinity binding sites for [3H]cytochalasin B; the number of sites detected was on the order of about one per actin filament (one site/500 actin monomers). This number remained unchanged when the actin (prepared by polymerization-depolymerization cycles) was further purified by ion exchange and gel filtration chromatography. Competitive displacement experiments showed that the relative affinity of several cytochalasins for these sites corresponds to their relative effectiveness in inhibiting actin polymerization induced by F-actin. These results suggest that actin filaments can accelerate the rate of polymerization of G-actin in low ionic strength medium by providing sites onto which actin monomers can be added, and that cytochalasins inhibit actin filament elongation by binding to high affinity sites located at the polymerization end of the filaments.
我们发现，在低离子强度介质中，向球状肌动蛋白（G-肌动蛋白）溶液中添加少量丝状肌动蛋白（F-肌动蛋白）会导致G-肌动蛋白快速聚合。细胞松弛素的亚化学计量水平（相对效力：细胞松弛素D大于细胞松弛素E约等于细胞松弛素B大于二氢细胞松弛素B）会抑制该反应。结合实验表明，F-肌动蛋白而非G-肌动蛋白含有[3H]细胞松弛素B的高亲和力结合位点；检测到的位点数量约为每条肌动蛋白丝一个（一个位点/500个肌动蛋白单体）。当通过离子交换和凝胶过滤色谱进一步纯化（通过聚合-解聚循环制备的）肌动蛋白时，该数量保持不变。竞争性置换实验表明，几种细胞松弛素对这些位点的相对亲和力与其抑制F-肌动蛋白诱导的肌动蛋白聚合的相对有效性相对应。这些结果表明，肌动蛋白丝可通过提供可添加肌动蛋白单体的位点来加速低离子强度介质中G-肌动蛋白的聚合速率，并且细胞松弛素通过与位于丝聚合末端的高亲和力位点结合来抑制肌动蛋白丝的伸长。
