Insight into the mechanism of fast movement of myosin from Chara corallina.

Chara myosin, two-headed plant myosin belonging to class XI, slides F-actin at maximally 60 μm s−1. To elucidate the mechanism of this fast sliding, we extensively investigated its mechanochemical properties. The maximum actin activated ATPase activity, Vmax, was 21.3 s−1 head−1 in a solution, but when myosin was immobilized on the surface, its activity was 57.6 s−1 head−1 at 2 mg ml−1 of F-actin. The sliding velocity and the actin activated ATPase activity were greatly inhibited by ADP, suggesting that ADP dissociation was the rate limiting step. With the extensive assay of motility by varying the surface density, the duty ratio of Chara myosin was found to be 0.49–0.44 from velocity measurements and 0.34 from the landing rate analysis. At the surface density of 10 molecules μm−2, Chara myosin exhibited pivot movement under physiological conditions. Based on the results obtained, we will discuss the sliding mechanism of Chara myosin according to the working stroke model in terms of its physiological aspects. aspects. Cell Motil. Cytoskeleton 2007. © 2006 Wiley-Liss, Inc.