In vivo phosphorylation of a cardiac myosin-like protein.

Cardiac myosin heavy chains synthesized in vivo were identified by labeling of N epsilon, N epsilon, N epsilon trimethyllysine with S-adenosyl-L-(methyl 3H) methionine. A similar assessment of in vivo phosphorylation of this myosin fraction indicated that phosphate incorporation may not be occurring in cardiac myosin heavy chains, but rather in another cardiac myosin-like protein which co-purifies with myosin heavy chains.