The intermediary stages of the metabolism of endogenous protein have been the subject of considerable interest from the time of the earliest studies on the physiology and biochemistry of nutrition. Recently interest has been renewed or accentuated because of the increasing recognition of the importance of hypoproteinemic states in clinical medicine. The recent attempts by Elman, Farr and others1 to build up tissue and plasma protein by supplying protein precursors intravenously emphasized the need for greater knowledge concerning the utilization of these materials by the organism.
One of the least understood phases in this endogenous cycle is the fate of the protein-split products released by catabolism of tissue protein. It is important to know whether these products are available, wholly or in part, for the repair of damaged tissues and for the replenishment of protein stores in the liver and the circulating plasma.
Madden and Whipple and co-workers2