Protein Synthesis and RNA in Tissues of the Pig

The rate of protein synthesis in 75-kg pigs was measured by continuous intravenous infusion of [14C]tyrosine. In the whole body, over 600 g of protein were synthesized each day. In pigs, rats, and man the rate of protein synthesis in the whole body was related to metabolic rate. The fractional rate of synthesis of protein in the tissues was also measured. The proteins of visceral organs (liver kidney, lung, and spleen) were renewed at rates close to 20% per day, those of brain at 8% per day, heart 7% per day, and skeletal muscle 4% per day. A significant correlation was observed between the fractional rate of protein synthesis in the tissue and RNA concentration. Calculation of the total amount of protein synthesized in skeletal muscle of the pig (fractional rate of synthesis X protein content) shows that muscle contributes 42% of whole-body synthesis. By contrast, in the rat only 19% of whole-body synthesis occurs in muscle.