Effects of insulin and glucagon on the incorporation of [14C]glycine into the protein of the liver and opercular muscle of the eel in vitro.

Effects of insulin and glucagon on the incorporation of [14C]glycine into the protein of liver slices and the opercular muscle of the eel were studied in vitro. Addition of insulin (0.1 IU/ml) to the medium increased the radioactivity both of the trichloroacetic acid (TCA)-soluble fraction and of the protein of the opercular muscle, indicating an acceleration by the hormone both of entry of the amino acid into the tissue and of protein synthesis. Insulin also increased the incorporation of [14C]glycine into the liver protein, while a decrease in the radioactivity of the TCA-soluble fraction was observed. These findings suggest that the hormone accelerated protein synthesis at the expense of an intracellular amino acid pool. In contrast, glucagon (5 micrograms/ml) did not affect the radioactivity either of the TCA-soluble fraction or of protein for either the opercular muscle or the liver. Thus, the present results highlight the importance of insulin in the regulation of protein synthesis in the eel both in muscle and in liver.