Light chain phosphorylation alters the conformation of skeletal muscle myosin

Using limited proteolysis by chymotrypsin or papain, we examined the effects of phosphorylation on the conformation of skeletal muscle myosin. In the absence of MgCl₂, phosphorylation of the 19,000 dalton light chain (LC₂) inhibited digestion of LC₂ by chymotrypsin or papain. Phosphorylation also suppressed chymotryptic conversion of the heavy chain to subfragment 1 and increased its conversion to heavy meromyosin. These results indicate that phosphorylation alters the conformation of the N-terminal segment of LC₂ and suggest that it also affects the heavy chain. In the presence of MgCl₂, phosphorylation inhibited the chymotryptic digestion of LC₂ but an effect on digestion of the heavy chain was not apparent. Thus, phosphorylation of LC₂ alters LC₂ conformation under physiological conditions.