title: Orientational order parameter of the nematic liquid crystalline phase of F-actin.
abstract: We measured the orientational order parameter of F-actin traversing the isotropic-nematic phase transition using a combination of techniques, including fluorescence imaging, local birefringence measurements, and small-angle x-ray scattering. The order parameter approaches a saturated value of 0.75 for actin concentrations above the region of the isotropic-nematic phase transition. This result implies a significant extent of misalignment and consequently entanglement among long actin filaments, even in the nematic phase. We determine the specific birefringence of completely aligned F-actin to be Deltan(0)=2.3 x 10(-5) ml/mg. At concentrations slightly below the isotropic-nematic transition, nonzero values of the order parameter are detected for hours following an initial alignment, indicating extremely slow rotational kinetics of F-actin in the entangled networks.
authors.affiliation: Department of Physics, Brown University, Providence, Rhode Island 02912, USA.
authors.forename: Jorge
authors.initials: J
authors.lastname: Viamontes
authors.forename: Suresh
authors.initials: S
authors.lastname: Narayanan
authors.forename: Alec R
authors.initials: AR
authors.lastname: Sandy
authors.forename: Jay X
authors.initials: JX
authors.lastname: Tang
mesh_terms: D008841:Actin Cytoskeleton / Q000737:chemistry*; D000199:Actins / Q000737:chemistry*; D000818:Animals; D018360:Crystallography, X-Ray; D050866:Liquid Crystals / Q000737:chemistry*; D018482:Muscle, Skeletal / Q000737:chemistry; D044367:Phase Transition; D011817:Rabbits
chemical_list: D000199:Actins