1: Adv Exp Med Biol  1988;226:267-76 

Optical anisotropy decay studies of the dynamic structure of myosin filaments.

Ishiwata S, Kinosita K Jr, Yoshimura H, Ikegami A.

Department of Physics, School of Science and Engineering, Waseda University,
Tokyo.

We applied flash-induced absorption and phosphorescence anisotropy decay methods
to the study of rotational motions of myosin heads in solution), myofibrils and
muscle fibers); myosin heads were selectively labeled with a triplet probe EMI
(5-eosinylmaleimide). EMI-labeled subfragment 1 (S1) showed a single exponential
decay of anisotropy over two decades; the analysis indicated that if S1 is
modeled as a prolate ellipsoid of revolution, the major axis was 16-17 nm and
the minor axis 4.7-4.5 nm. The decay curve of myosin filaments could be
simulated by double-exponentials-plus-constant approximation. The data could be
analyzed by a double-cone model), in which we assumed that a head part (S1),
wobbles in the first cone and a rod portion next to the head also wobbles in the
second cone. The semiangle of each cone was estimated to be 35 and 48 degrees,
respectively. We found that myosin heads in myofibrils under relaxing conditions
extensively rotated as in myosin filaments in solution. When the spacing between
thick and thin filaments was artificially reduced by the increase of osmotic
pressure with the addition of polyvinylpyrrolidone (PVP), restriction of the
angular range of the rotational motion was observed. Under rigor conditions no
motion was observed in a 10 microsecond time scale, indicating that the heads
were immobilized by binding to thin filaments. Preliminary results on the
rotational motions of myosin heads in muscle fibers are also reported.

PMID: 3044018 [PubMed - indexed for MEDLINE]