Metabolism of myofibrillar proteins in the normal and hypertrophic heart.

The pathways of myofibrillar assembly and degradation were studied in normal heart and during developing hypertrophy by two independent methods: amino acid incorporation kinetics and the double isotope technique. The validity and sensitivity of both methods were evaluated by computer analysis of data for which leucyl-tRNA was used as a protein precursor. The data obtained indicate that the myofibrillar proteins turn over at nonuniform rates. The half-lives of the proteins studied increase as follows: myosin HC = alpha-actin = tropomyosin greater than LC1 = LC2 greater than actin. In the case of light chains, a macromolecular precursor pool was detected which contributes to the observed lower labeling with 3H-leucine. During developing hypertrophy, the rate of light-chain labeling is increased relative to that of heavy chains.