4851 VISCOELASTIC MODULI OF STERICALLY AND CHEMICALLY CROSS-LINKED ACTIN NETWORKS IN THE DILUTE TO SEMIDILUTE REGIME - MEASUREMENTS BY AN OSCILLATING DISK RHEOMETER O. Muller, HE. Gaub, (gaub@lmu.de
)M. Barmann, E. Sackmann, (sackmann@ph.tum.de
) Macromolecules
(1991-05-27) 24-11 p.3111 PubMed Publisher : AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA. ISSN : 0024-9297Abstract : Measurements of the frequency dependence of the storage modulus G'(omega) and the loss modulus G"(omega) of sterically and chemically cross-linked actin networks employing a rotating disk rheometer at low frequencies (0.0004-1 Hz) are reported. By magnetically driven oscillations of a disk deposited on the surface of the solutions and by suppression of the gelation of actin at the exposed air/water interface by lipid monolayers, measurements in the dilute to semidilute concentration regime were performed in order to get insight into the internal dynamic of the actin filaments. The frequency dependencies of the viscoelastic moduli of F-actin closely resemble those of high molecular weight polymer solutions exhibiting (i) a viscous flow at omega < tau-d-1 (where tau-d corresponds to the terminal relation time), (ii) a rubber plateau at tau-d-1 less-than-or-equal-to omega less-than-or-equal-to tau-e-1, and (iii) a Rouse-like regime at omega > tau-e-1. G'(omega) and G"(omega) scale as omega-0.5 in the latter regime, which demonstrates a high degree of chain flexibility. G'(omega) and G"(omega) versus frequency curves were recorded as a function of the actin concentration and contour length (adjusted by the actin binding protein severin). Power laws for the actin concentration (c(A)) dependence of the plateau value of the storage modulus G(N)0 and the concentration and length dependence of the terminal relaxation time tau-d were obtained. At high concentrations (volume fractions phi > 10(-4)), we find G(N)0 proportional c(A) 1.9+/-0.2 whereas a linear law holds below this limit in agreement with the behavior of dilute to semidilute polymer solutions. tau-d scales as c(A)4 in the entangled regime and as c(A) in the semidilute regime. For the contour length dependence, we found tau-d proportional L5 and tau-d proportional L, respectively. The persistence (or segment) length of the actin filaments was determined in two independent ways as L(p) = 0.1-0.3-mu-m in agreement with electron microscopic studies of filaments capped by severin. The contour length (L proportional molecular weight) was determined from the limiting concentration of the dilute to semidilute transition as L almost-equal-to 50-mu-m. Measurements of G'(omega) and G"(omega) of actin filaments chemically cross-linked by alpha-actinin and the 120-kD gelation factor of Dictyostelium discoideum were performed. The viscoelastic moduli are only slightly changed if the average distance between (chemical) cross-links, L(i), is larger than the mesh size, xi, of the actin network, whereas G' and G" increase strongly for L(i) < xi, suggesting local segregation into sol-like and gel-like phases (microgel formation). The elastic modulus G' decreases with increasing temperature if L(i) < xi (anomalous behavior) but increases again for L(i) > xi as in the case of the transient networks. The anomalous behavior is explained in terms of a thermally induced gel-sol transition at low degrees of cross-linking. Corresponding Author : Affiliation(s) : (0) TECH UNIV MUNICH,DEPT PHYS,BIOPHYS LAB,JAMES FRANCK STR,W-8046 GARCHING,GERMANY.;Key words : F-ACTIN; MECHANICAL-PROPERTIES; DICTYOSTELIUM-DISCOIDEUM; BINDING PROTEIN; FLEXIBILITY; GELS; COMPLEXES Type : Article, English. 1991-05-27Time cited 56; Journal impact factor for year 1994 equals 3.016Scientific Domain: Activity: Micromanipulation Technique: Visualization Technique: Mark as do not mark Not defined 
