Comparative Growth on Diets Containing Ten and Nineteen Amino Acids, With Further Observations Upon the Rôle of Glutamic and Aspartic Acids

In a series of papers extending over many years evidence has been presented regarding the nutritive r&e of each of the recognized components of proteins.The results have demonstrated that ten amino acids are essential dietary components for the rat.The exclusion from the food of any one of these, other than arginine, leads to a profound nutritive failure, loss in weight, and eventual death.Arginine differs in several respects from other constituents of proteins.First, it can be synthesized by the rat (l), but not at a rate commensurate with the needs of the organism for maximum growth.Thus, young animals which are deprived of arginine gain much less rapidly than do their litter mates which receive this amino acid (2).Because of this fact, arginine is classified in this laboratory as an essential component of the food.On the other hand, arginine is unique in that it can be replaced in part for growth purposes by proline or glutamic acid, though not by hydroxyproline (3).These relationships are believed to be associat,ed with the ability or inability of the organism to effect the interconversion of the amino acids in question (cf.(3-6)).In connection with the above studies two points require further consideration.The first has to do with the nutritive efficiency of diets in which t,he ten essential amino acids are virtually the sole sources of nitrogen.The second relates to the precise status of glutamic acid as a growth stimulant in the presence of arginine.No data have been presented from this laboratory regarding the comparative growth behavior of animals receiving mixtures of ten and nineteen amino acids.Several years ago, experiments of this nature were conducted under the most favorable conditions then possible.At that time, the conclusion was reached, and stated on several occasions without t,he submission of evidence (7, S), that animals upon such simplified diets gain in weight as rapidly as they do when all of the com-