Stabilization of actin filaments in the presence of urea

Hatori, K., Nomua, N.

Department of Bio-System Engineering, Yamagata University


We examined the stabilization of actin filaments, the polymerization from monomers into the filaments and sliding movement on myosin molecules in the presence of urea, which could act as a denaturant to modify the structure of proteins. Under a fluorescent microscopy, rhodamine-phalloidin-labeled actin filaments were observed for measuring its length distribution. The mean value of the filament length increased with an increase of urea concentration up to 0.8 M. The sliding velocity of actin filaments on myosin molecules gradually decreased as the urea concentration was increased, and then was completely suppressed at 0.8 M of the concentration. In addition, when the polymerization from actin monomers into the filament was directly observed, the polymerization rate rapidly decreased from 0.07 to 0.002 um/min in the concentration range of 0-0.8 M. Actin properties were found to be significantly influenced by the presence of urea at the specific concentration of 0.8 M. Once actin molecules form into the filament, the filamental structure may be reinforced by alteration in behavior of water molecules around the filament.