MG-ACTIN AND CA-ACTIN FILAMENTS APPEAR VIRTUALLY IDENTICAL IN STEADY-STATE AS DETERMINED BY DYNAMIC LIGHT-SCATTERING

Dynamic light scattering measurements show that although Mg-actin poly merizes more rapidly than Ca-actin (actin at 0.04-0.4 mg/ml polymerize d with 0.1 M KCl +/- 2 mM MgCl2 or CaCl2, at room temperature or at 10 degrees C), steady-state filaments exhibit nearly identical intensity autocorrelation functions and similar mean scattered intensities. The dynamic data are used to measure the persistence length of the filame nts which is found to be 4.2 mu m independent of the bound cation and of the actin concentration.