Synthesis and phosphorylation of canine cardiac myosin in tissue-culture assessment of hypertrophying factors.

Canine cardiac myosin, which was synthesized in a 14-day tissue culture, based on L-[3H] leucine incorporation, was precipitated with goat gamma G antimyosin (cardiac-specific) and analyzed on dodecylsulfate gels. Incorporation of 32PO4 into myosin chains occurring in culture was the same as that obtained in vivo and appeared to be coupled with translation. Removal of 32PO4 from myosin heavy chains with base treatment indicated the presence of phosphoserine and phosphothreonine in canine cardiac myosin heavy chains. Further acid hydrolysis confirmed the data. The system described here, i.e., analyses of 32PO4 and L[3H] leucine incorporation into myosin heavy chains, could be used as a system for assaying hypertrophying factors.