Behaviour of sonicated actin polymers: Adenosine triphosphate splitting and polymerization

Abstract

The ATP splitting rate, the viscosity and other properties of actin solutions under and after sonic vibration have been investigated at various concentrations of actin and salts. It was found that under sonic vibration at low salt concentrations, G-actin coexists with short actin polymers and the equilibrium between them can be expressed as a kind of condensation phenomena, as in the case of the ordinary G-F transformation of actin. The critical concentration of G-actin for polymers under sonic vibration is almost the same as that for the ordinary Factin under the same solvent conditions. The steady and rapid ATP splitting in actin solutions under sonic vibration, which is proportional to the concentration of polymers, is interpreted as a result of the cyclic polymerization-depolymerization of G-actin taking place at a large number of ends of short polymers, where the polymerization is coupled with the ATP splitting. Sonic vibration accelerates polymerization and depolymerization probably by the increase in the number of ends of polymers. The increase in viscosity of sonicated actin after stopping vibration is mainly due to association of short polymers to form long F-actin.