[Asynchronous turnover of the thin filament proteins, actin, tropomyosin and troponin by a continuous double isotope method].

The relative turnover rate of protein components of the thin filament was measured by a continuous double isotope method. Both 3H-lysine and 14C-lysine were administered continuously in the diet to male adult rabbits for 7 days. On the 7th day, the 14C-lysine was discontinued while the 3H-lysine was continued for 14 additional days. The relative turnover rate of the protein components was estimated from the 3H/14C ratios of the isolated protein of the same animal. From the different ratios of 3 H/14C of each protein fraction, asynchronous turnover of the thin fila ment proteins (actin, tropomyosin and troponin) was concluded. The order of degree in relative turnover rate is as follows: troponin> tropomyosin>actin.