Dynamics of F-actin and F-actin/filamin networks as studied by photon correlation spectroscopy.

Photon correlation spectroscopy was used to study both F-actin and F-actin/filamin networks in solution. The measured autocorrelation functions were analyzed with the inverse Laplace transform CONTIN. The resulting frequency distributions consist of maximal five relatively narrow peaks. This rather unexpected finding disagrees with the frequency spectra calculated for an entangled rigid rod model. For this model, we expect spectra consisting of a single broad peak. Factors like flexibility, deviation from an experimental length distribution, interference with chemical reactions, and translation-rotation coupling that would influence the profile of the frequency distribution could be excluded by comparison of the data with model calculations or qualitative estimates. We conclude that our data for F-actin are consistent with the dynamics of an infinite network stable on the time scale of the observed modes. Further support for this interpretation is provided by a comparison with frequency spectra of actin/filamin networks. These appear to be very similar in shape. The main peak of these spectra that corresponds to the slow motions shifts to lower frequencies with increasing cross-link density. It appears that higher frequency modes of the gel are more efficiently damped with progressive cross-link density, resulting in a predominance of the slow motions in the spectra. This behavior has been already found in other systems and seems to be a general feature of cross-linked systems.