Correlation between lability and relative turnover rate of soluble protein of the rat liver

A study was made on whether or not the lability of protein generally correlates with its metabolic turnover rate. Two fractions of soluble protein were prepared from rat liver. Using the double isotope method, it was revealed that fraction precipitated with half-saturated ammonium sulfate had a larger turnover rate than the supernatant one. Both dietary protein depletion and starvation, though they significantly decreased total protein content, did not affect the ratio of the amount of protein in the precipitate to that of the supernatant fraction. These results suggested that both fractions, though they had a different turnover rates, were equally influenced by dietary protein depletion or fasting. In consequence, the results imply that the lability of protein does not necessarily in parallel with the metabolic turnover rate.