Fluctuation of local points of F-actin sliding on the surface-fixed H-meromyosin molecules in the presence of ATP

F-actin fragments fluorescently labeled with rhodamine-phalloidin were copo lymerized with non-labeled F-actin fragments. F-actin copolymer consisted o f several bright (fluorescent) and dark (non-fluorescent) stripes of approx imately 1 mum in width. Local motion of individual speckled F-actin was inv estigated by measuring translocation fluctuation of several tracing points marked on the actin filament. The tracing points included the borders betwe en neighboring bright and dark stripes, as well as the tip and tail of the filament. For speckled F-actin with an average sliding speed of 4.6 mum/s a t 23 degreesC, the translocation distance of the tracing points (per 0.1 s) showed significant fluctuation, of the order of +/-0.12 mum/s, approximate ly 25% of the sliding speed. The fluctuation correlation of the translocati on distance between two tracing points decreased as the distance between th em increased. Statistical analysis of the correlation length of the translo cation distance L, showed that L, increased with the sliding speed of the a ctin filament. The sliding speed, however, saturated as the correlation len gth became close to the persistence length of the bending elasticity of F-a ctin. On the contrary, the correlation length of change in the translocatio n direction was essentially equal to the persistence length of F-actin, ind ependent of the sliding speed. These results suggest that elasticity of the actin filament underlies the sliding velocity of F-actin. (C) 2001 Elsevie r Science B.V. All rights reserved.