Contractile and protractile coordination within an actin filament sliding on myosin molecules

An actin filament exhibits distortions longitudinally when it slides upon m yosin molecules. We observed that the actin filament demonstrated contracti le distortions at low ATP concentrations and protractile distortions at hig h concentrations. Temporal development of such distortions was identified, by tracing each of several speckled fluorescent markers attached to the act in filament. Close association of the sliding movement to the moving distor tions of an actin filament suggests the presence of a unitary mechanism reg ulating the apparently two different modes of dynamic movement. (C) 1999 El sevier Science B.V. All rights reserved.