Ando T, Scales D
J Biol Chem. 1985 Feb 25;260(4):2321-7.
As is well known, the light scattering intensity of F-actin solutions increases immediately upon formation of the rigor complex with subfragment-1 (S-1). We have found that after the initial rise in scattering, there is a further gradual increase in scattering (we call it "super-opalescence"). Fluorescence and electron microscopic observations of acto-S-1 solutions showed that super-opalescence results from formation of actin filament bundles once S-1 binds to F-actin. The actin bundles possessed transverse stripes with a periodicity of about 350 A, which suggested that in the bundles actin filaments are arranged in parallel register. The rate of the initial process of bundle formation (i.e. side-by-side dimerization) could be approximately estimated by measuring the initial rate of super-opalescence (V0). V0 had a maximum (V0m) at a molar ratio of S-1 to actin of 1;6-1;7, regardless of the actin concentration, pH (6-8.5), Mg2+ concentration (up to 5 mM), or ionic strength (up to 0.3 M KC1). Lower pH, higher Mg2+ concentration, and higher ionic strength increased V0m; V0 was proportional to the square of the actin concentration, regardless of the solution conditions.
众所周知，F-肌动蛋白溶液与亚片段-1（S-1）形成强直复合物后，其光散射强度会立即增加。我们发现，在散射最初升高之后，散射会进一步逐渐增加（我们称之为“超乳光”）。对肌动蛋白-S-1溶液的荧光和电子显微镜观察表明，一旦S-1与F-肌动蛋白结合，超乳光就源于肌动蛋白丝束的形成。肌动蛋白束具有周期性约为350埃的横向条纹，这表明在束中肌动蛋白丝是平行排列的。束形成的初始过程（即并排二聚化）的速率可以通过测量超乳光的初始速率（V0）大致估算出来。无论肌动蛋白浓度、pH值（6 - 8.5）、Mg²⁺浓度（高达5 mM）或离子强度（高达0.3 M KCl）如何，V0在S-1与肌动蛋白的摩尔比为1:6 - 1:7时具有最大值（V0m）。较低的pH值、较高的Mg²⁺浓度和较高的离子强度会增加V0m；无论溶液条件如何，V0与肌动蛋白浓度的平方成正比。
