1: J Biochem (Tokyo)  1994 Apr;115(4):644-7 

Stepwise motion of an actin filament over a small number of heavy meromyosin
molecules is revealed in an in vitro motility assay.

Miyata H, Hakozaki H, Yoshikawa H, Suzuki N, Kinosita K Jr, Nishizaka T,
Ishiwata S.

Department of Physics, Faculty of Science and Technology, Keio University,
Kanagawa.

In order to determine the relative motions of an actin filament and a myosin
molecule upon hydrolysis of one ATP, an in vitro motility assay, in which
individual actin filaments slide over heavy meromyosin molecules bound to a
substrate, was combined with an optical trapping technique. An actin filament,
attached to a gelsolin-coated bead, was captured with an optical trap. The
surface-bound heavy meromyosin molecules pulled the filament against the
trapping force, which resulted in back and forth motions of the actin-bound
bead. The number of heavy meromyosin molecules interacting with an actin
filament (at most 1/micron filament) and the ATP concentration (< or = 0.5
microM) were chosen so as to facilitate detection of each "pull." Calculation of
the centroid of the bead image revealed abrupt displacements of the actin
filament. The frequency of such displacements was between 0.05 and 0.1 per 1 s
per 1 micron actin filament, being consistent with calculated values based on
the reported bimolecular binding constants of ATP and the actomyosin rigor
complex. The distribution of the displacements peaked around 7 nm at a trapping
force of 0.016 pN/nm, but it became broader, and some displacements were as
large as 30 nm, when the trapping force was reduced to 0.0063 pN/nm, suggesting
that the force generation due to the structural change of a myosin head may be
insufficient to explain such displacements.

PMID: 8089077 [PubMed - indexed for MEDLINE]