Role of the free amino acid pool of the intestine in protein synthesis

1. The accumulation of glycine and its incorporation into protein have been studied in rat intestinal slices in vitro. 2. Pyridoxal HCl, which raises intracellular pool concentration of glycine, similarly increases the rate of glycine incorporation into protein. 3. Kinetic data demonstrates a lag in glycine incorporation into protein, suggesting that the glycine passes through an intracellular pool (or pools) before its incorporation into protein. 4. In vivo experiments using leucine demonstrate that specific activity in the protein is a reflection of the specific activity of the soluble "pool" of leucine. 5. These data are consistent with a model in the intestinal mucosa in which glycine in the extracellular pool is not the direct precursor for protein synthesis, but suggest that glycine and perhaps other amino acids first pass through some intracellular pool(s).