This project is a study of the regulatory responses made by the liver to changes in amino acid supply from the diet. The research program forcusses on parallel changes in the protein, RNA and phospholipid content of the liver resulting from changes in the protein content of the diet, and concentrates on acute changes in liver metabolism caused by alterations in amino acid supply, hopefully providing an integrated picture. Among the responses of the liver to amino acid supply to be examined will be: (a) The regulation of purine biosynthesis; (b) The synthesis of nuclear RNA; c) Mitochondrial RNA and poly A synthesis; (d) Synthesis of retained and secreted liver proteins, and the regulation of ER membrane in relation to amino acid supply. (e) The special role of tryptophan supply in these processes, and the significance of the binding of free tryptophan to serum albumin and to tissue proteins in its function.