Key words: fast and slow skeletal muscle myosin, myosin filaments, Ca 2+ -induced structural transitions, method of slow skeletal muscle myosin preparation. In the previous study (Podlubnaya et al., 1999, J. Struc. Biol. 127, 1-15) Ca 2+ -induced reversible structural transitions in synthetic filaments of pure fast skeletal and cardiac muscle myosins were observed under rigor conditions (-Ca 2+ /+ Ca 2+ ). In the present work these studies have been extended to new more order-producing conditions (presence of ATP in the absence of Ca 2+ ) aimed at arresting the relaxed structure in synthetic filaments of both fast and slow skeletal muscle myosin. Filaments were formed from column-purified myosins (rabbit fast skeletal muscle and rabbit slow skeletal semimebranosus proprius muscle). In the presence of 0.1 mM free Ca 2+ , 3 mM Mg 2+ and 2 mM ATP (activating conditions) these filaments had a spread structure with a random arrangement of myosin heads and subfragments 2 protruding from the filament backbone. Such a structure is indistinguishable from the filament structures observed previously for fast skeletal, cardiac (see reference cited above) and smooth (Podlubnaya et al., 1999, J. Muscle Res. Cell Motil. 20, 547-554) muscle myosins in the presence of 0.1 mM free Ca 2+ . In the absence of Ca 2+ and in the presence of ATP (relaxing conditions) the filaments of both studied myosins revealed a compact ordered structure. The fast skeletal muscle myosin filaments exhibited an ax-Vol. 47 No. 4/2000 1007-1017 QUARTERLY .
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.