Dynamic light scattering study of muscle f-actin

By use of digital autocorrelation and fast Fourier methods, dynamic light-scattering studies of in vitro reconstituted muscle F-actin were made over a wide range of concentrations. 0.01-2 mg ml F-actin. Measurements of correlation function [g¹(t)]² showed that a transition from a dilute to a semidilute regime for the Brownian motions of filaments occurred at around 0.3 mg ml F-actin. Beyond this concentration, profiles of successively measured [g¹(t)]² showed very poor reproducibility. This resulted from the existence of very slow components, which could not be measured with a high statistical accuracy even for a measuring time of 3600 s/run. On the other hand, subtraction of these components automatically by an electronic circuit, [g^-1(t)]², or by computer processing, [g¹(t)]², resulted in a fairly good reproducibility of the profies, The decay c of [g^-1(t)]² (and [g^-1(t)]²) were very similar to those of [g¹(t)]² for dilute solutions. A theoret which could account for the above situation. The time sequence {n(t,T)} of photoelectron counts at a sampling time T of light scattered from semidilute solutions of F-actin was stored on magnetic tapes, and both power spectra S̄(f) and correlation functions [g^-1(t)]² were computed by taking the ensemble average over many short records with duration 1024T. Since both S̄(f and [g^-1(t)]² lacked frequency components lower than 1 (2048T) Hz. their profiles were highly reproducible. An of S̄(f) confirmed our earlier results which had shown an apparent contradiction to later results by a correlation method. A comparison of S̄(f) and [g^-1(t)]² based on the same {n(t,T)} clarified the reasons why the bandwidth Γ of S̄( differed from the bandwidth \ ̄gG of [g¹(t)]² and [g^-1(t)]². The temperature dependence of Γ suggested that F-actin flexible and that the flexibility parameter would change with temperature.