title: Definite differences between in vitro actin-myosin sliding and muscle contraction as revealed using antibodies to myosin head.
abstract: Muscle contraction results from attachment-detachment cycles between myosin heads extending from myosin filaments and actin filaments. It is generally believed that a myosin head first attaches to actin, undergoes conformational changes to produce force and motion in muscle, and then detaches from actin. Despite extensive studies, the molecular mechanism of myosin head conformational changes still remains to be a matter for debate and speculation. The myosin head consists of catalytic (CAD), converter (CVD) and lever arm (LD) domains. To give information about the role of these domains in the myosin head performance, we have examined the effect of three site-directed antibodies to the myosin head on in vitro ATP-dependent actin-myosin sliding and Ca2+-activated contraction of muscle fibers. Antibody 1, attaching to junctional peptide between 50K and 20K heavy chain segments in the CAD, exhibited appreciable effects neither on in vitro actin-myosin sliding nor muscle fiber contraction. Since antibody 1 covers actin-binding sites of the CAD, one interpretation of this result is that rigor actin-myosin linkage is absent or at most a transient intermediate in physiological actin-myosin cycling. Antibody 2, attaching to reactive lysine residue in the CVD, showed a marked inhibitory effect on in vitro actin-myosin sliding without changing actin-activated myosin head (S1) ATPase activity, while it showed no appreciable effect on muscle contraction. Antibody 3, attaching to two peptides of regulatory light chains in the LD, had no significant effect on in vitro actin-myosin sliding, while it reduced force development in muscle fibers without changing MgATPase activity. The above definite differences in the effect of antibodies 2 and 3 between in vitro actin-myosin sliding and muscle contraction can be explained by difference in experimental conditions; in the former, myosin heads are randomly oriented on a glass surface, while in the latter myosin heads are regularly arranged within filament-lattice structures.
authors.affiliation: Department of Physiology, School of Medicine, Teikyo University, Tokyo, Japan.
authors.forename: Haruo
authors.initials: H
authors.lastname: Sugi
authors.affiliation: Department of Integrated Sciences in Physics and Biology, College of Humanities and Sciences, Nihon University, Tokyo, Japan.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Chaen
authors.affiliation: Department of Electronic Engineering, Shibaura Institute of Technology, Tokyo, Japan.
authors.forename: Takakazu
authors.initials: T
authors.lastname: Kobayashi
authors.affiliation: Department of Electronic Engineering, Shibaura Institute of Technology, Tokyo, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Abe
authors.affiliation: Department of Electronic Engineering, Shibaura Institute of Technology, Tokyo, Japan.
authors.forename: Kazushige
authors.initials: K
authors.lastname: Kimura
authors.affiliation: Department of Physiology, School of Dentistry, Tsurumi University, Yokohama, Japan.
authors.forename: Yasutake
authors.initials: Y
authors.lastname: Saeki
authors.affiliation: Department of Physiology, School of Dentistry, Tsurumi University, Yokohama, Japan.
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Ohnuki
authors.affiliation: Department of Applied Biochemistry, Graduate School of Agriculture and Life Sciences, University of Tokyo, Tokyo, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Miyakawa
authors.affiliation: Department of Applied Biochemistry, Graduate School of Agriculture and Life Sciences, University of Tokyo, Tokyo, Japan.
authors.forename: Masaru
authors.initials: M
authors.lastname: Tanokura
authors.affiliation: Graduate School of Frontier Sciences, University of Tokyo, Tokyo, Japan.
authors.forename: Seiryo
authors.initials: S
authors.lastname: Sugiura
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000199:Actins / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000911:Antibodies, Monoclonal / Q000032:analysis*; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism; D009038:Motion; D009119:Muscle Contraction; D018485:Muscle Fibers, Skeletal / Q000737:chemistry / Q000378:metabolism*; D009218:Myosins / Q000737:chemistry* / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011817:Rabbits
chemical_list: D000199:Actins; D000911:Antibodies, Monoclonal; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D009218:Myosins; D008274:Magnesium; D002118:Calcium