Viscosity of G-ADP and G-ATP actin

Abstract

The intrinsic viscosities of several preparations of G-ADP actin and G-ATP actin have been measured at 0 °. An intrinsic viscosity of 3.7 ml per gram was found for G-ADP actin in the presence of 0.1 or 0.2 m monovalent salt. In 0.1 m m MgCl 2, using Cannon Master viscometers, an intrinsic viscosity of about 5 ml per gram was obtained for G-ADP and G-ATP actin, suggesting identical conformations for the two molecules. These viscosities are substantially lower than those previously reported for globular actin, and indicate axial ratios between 1 and 4. These values provide direct confirmation from actin in solution for the shape of the globular actin obtained from electron micrographs by Hanson and Lowy and by Rowe.