MEASUREMENT OF THE RATE OF WHOLE-BODY PROTEIN-SYNTHESIS BY INTRAPERITONEAL INJECTION OF A LARGE DOSE OF ALANYLTYROSINE WITH [C-14] TYROSINE

The rate of whole body protein synthesis in mice was obtained by a newly modified large dose method. A large amount of alanyltyrosine was injected intraperitoneally together with a tracer dose of [14C]tyrosine into mice. The animals were sacrificed at 10, 17, 24 and 31 min after the injection. The specific radioactivity of free tyrosine in the whole body was slightly higher than in the serum at 10 min and then decreased linearly. The two straight lines from the serum and whole body crossed each other at about 20 min after the injection. The specific radioactivity of the bound tyrosine in the whole body homogenate increased linearly from zero. Assuming the specific radioactivity of free tyrosine at the crossover point represents that of the site of protein synthesis, we estimated the fractional rate of whole body protein synthesis in mice receiving diets containing egg white hydrolysate, or an amino acid mixture simulating egg white protein, by measuring the specific radioactivity of the free and proteinbound tyrosine at 20 min after the injection in another set of experiments. The fractional synthesis rate of whole body protein was 26.5%per day in the peptide-fed animals, and 19.7%per day in the amino acid-fed ones. The former value was significantly higher than the latter one. © 1990 by the Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.