FORMATION OF LIQUID-CRYSTALLINE PHASE OF ACTIN FILAMENT SOLUTIONS AND ITS DEPENDENCE ON FILAMENT LENGTH AS STUDIED BY OPTICAL BIREFRINGENCE

We studied the formation and structure of liquid crystalline phase of F-action solutions by polarized light photometry, assuming the a small domain of the liquid crystalline phase works as a linear retardation plate. Transmittance of polarized light due to the birefringence of liquid crystalline phase appeared above a threshold concentration of F-action. The threshold increased with a decrease in filament length, which was regulated by calcium-activated gelsolin. The intensity increased linearly with increasing concentrations until it reached a stationary value. The deviation of optical axis direction of the putative retardation plate was estimated 7-15 degrees. These results indicate that: (a) the liquid crystalline phase is formed above a threshold concentration of F-actin; (b) the threshold is proportional to the inverse of filament length; (c) the ordered phase coexists with the isotropic one, increasing the volume fraction with increasing concentrations until all filaments take the liquid crystalline structure; (d) the filaments in liquid crystalline phase take a highly ordered array. These results can be attributed to the excluded volume effect of rod-like molecules on the formation of liquid crystalline structure.