Effect of skeletal muscle myosin light chain 2 on the Ca2+-sensitive interaction of myosin and heavy meromyosin with regulated actin.
A low-speed centrifugation assay has been used to examine the binding of myosin filaments to F-action and to regulated actin in the presence of MgATP. While the cross-linking of F-actin by myosin was Ca2+ insensitive, much less regulated actin was cross-linked by myosin in the absence of Ca2+ than in its presence. Removal of the 19000-dalton, phosphorylatable light chain from myosin resulted in the loss of this Ca2+ sensitivity. Readdition of this light chain partially restored the Ca2+-sensitive cross-linking of regulated actin by myosin. Urea gel electrophoresis has been used to distinguish that fraction of heavy meromyosin which contains intact phosphorylatable light chain from that which contains a 17000-dalton fragment of this light chain. In the absence of Ca2+, heavy meromyosin which contained digested light chain bound to regulated actin in MgATP about 10-fold more tightly than did heavy meromyosin which contained intact light chain. The regulated actin-activated ATPases of heavy meromyosin also showed that cleavage of this light chain causes a substantial increase in the affinity of heavy meromyosin for regulated actin in the absence of Ca2+. Thus, the binding of both myosin and heavy meromyosin to regulated actin is Ca2+ sensitive, and this sensitivity is dependent on the phosphorylatable light chain.
D000199:Actins / Q000378:metabolism* / Q000494:pharmacology; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004533:Egtazic Acid / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D007700:Kinetics; D009132:Muscles / Q000032:analysis; D015879:Myosin Subfragments / Q000378:metabolism*; D009218:Myosins / Q000378:metabolism* / Q000502:physiology*; D011817:Rabbits
D000199:Actins; D015879:Myosin Subfragments; D004533:Egtazic Acid; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D009218:Myosins; D002118:Calcium