Synthesis of guinea-pig cardiac myosin as measured by constant infusion.

An equation was derived from which the turnover time of individual muscle proteins could be calculated from measurements made at a single time interval in individual animals after initiation of constant intravenous infusion of labelled amino acid. The calculation requires only the specific radioactivities of the amino acid in plasma, in the intracellular fluid and in the protein under study. Pool sizes were not required. When the equation was applied to adult guinea-pig cardiac myosin, the average turnover time was 16 +/- 1 days.