The role of the skeletal muscle myosin light chains N-terminal fragments

AbstractThe myosin regulatory and essential light chains in skeletal muscle do not play a role as significant as in scallop or smooth muscle, however, there are some data suggesting that the skeletal myosin light chains and their N-terminal parts may have a modulatory function in the interaction of actin with myosin heads. In this paper four conformational states of the myosin head with respect to the regulatory light chain bound cation (magnesium or calcium) and phosphorylation are proposed. Communication between regulatory and essential light chains and putative binding of the N-terminus of A1 essential light chain to actin is discussed

Factors influencing interaction of phosphorylated and dephosphorylated myosin with actin

The influence of various factors on the interaction of phosphorylated and dephosphorylated myosin with action was examined. It was found that the difference between the values of specific activity of the two myosin forms of actin-stimulated Mg 2+-ATPase is affected by changes in KCl, MgATP and acting concentration. The effect of increased pH on the differences in the rate of ATP hydrolysis by actomyosin containing phosphorylated myosin as compared with that of the dephosphorylated one, observed in the presence of EGTA, is abolished by addition of Ca 2+. Tropomyosin strongly inhibits the actin-stimulated Mg 2+-ATPase of phosphorylated myosin (by about 60%). The tropomyosin-troponin complex and native tropomyosin lowered the rate of ATP hydrolysis by actomyosin containing both phosphorylated and dephosphorylated myosin by about of 60% of the value obtained in the absence of those proteins. These results indicate that the change of negative charge on the myosin head due to phosphorylation and dephosphorylation of myosin light chains modulates the actin-myosin interaction at different steps of the ATP hydrolysis cycle. Phosphorylation of myosin seems to be a factor decreasing the rate of ATP hydrolysis by actomyosin under physiological conditions