Turnover Rate of Proteins in Liver Cellular Fractions of Rats Fed High Protein Diets

The effect of high protein intake on the turnover rate of the proteins as well as the protein content of liver cellular fractions has been studied in young rats. When rats fed diets containing high levels of casein, the protein content was increased in various cellular fractions of liver. The incorporation of intraperitoneally injected methionine-S³⁵ into the proteins of these fractions was in the following decreasing order: microsomal, supernatant, mitochondrial and nuclear fraction. The rate of disappearance of radioactivity in various fractions was not so much different from one another, but those of microsomal and supernatant fractions were slightly greater than those of the other fractions. The turnover rates of proteins in all cellular fractions and whole homogenate gradually elevated as the casein level in diets increasing from 25 to 60%. However, the inhancement occurred to a lesser degree than that in the turnover rate of liver proteins with increase in the casein level from zero to 25% which was reported previously.