title: Conformational transition in the myosin hinge upon activation of muscle.
abstract: We have determined the rates of chymotryptic proteolysis of the myosin hinge region in glycerinated rabbit psoas fibers and myofibrils in in rigor-inducing, activating, and relaxing buffers. The time course of formation of light meromyosin (LMM) provides a specific probe for cleavage within the hinge domain. In rigor-inducing and relaxing buffers proteolysis within the hinge is depressed, but on activation LMM is formed at a markedly increased rate, which is dependent on the concentration of MgATP. Peptide bond cleavage occurs at four widely separated sites spanning the length of the hinge domain. Only a trivial amount of proteolysis occurs at the head--rod swivel or within the heavy chain of the head itself (S-1 subunit) in rigor-inducing and relaxing solvents, and we find no significant change on activation. The rate of formation of LMM in rigor-inducing buffer is unchanged by addition of MgADP, Pi, or magnesium adenosine 5'-[beta, gamma-imido]triphosphate or in activating solvent at zero overlap between thick and thin filaments. These results provide evidence for a conformational (helix--coil) transition within the myosin hinge upon activation of skeletal muscle.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D007700:Kinetics; D008970:Molecular Weight; D009119:Muscle Contraction; D009132:Muscles / Q000378:metabolism*; D009210:Myofibrils / Q000378:metabolism; D009218:Myosins / Q000378:metabolism*; D011487:Protein Conformation; D011817:Rabbits
chemical_list: D000255:Adenosine Triphosphate; D009218:Myosins