Amino Acids as the Only Nitrogen Source During Growth and Differentiation.

Abstract

Experiments are in progress on forms lower than mammals to determine the value of isolated amino acids for protein synthesis and to ascertain which acids if any are essential for, or facilitate the growth of organisms of different phylogenetic levels, and which are of importance in the process of differentiation. An attempt has been made to bring tadpoles of Rana sylvatica to metamorphosis on a diet in which the only N available was the N of isolated amino acids. Carbohydrates, fats and vitamins were supplied in the form of a “Basal Diet”. The following amino acids were used in concentrations of 1% and 5%, added to the water: glycine, alanine, leucine, aspartic, glutamic, arginine, lysine, cystine, phenyl-alanine, tyrosine, tryptophane, proline, diiodo-tyrosine. Single acids and bi-acid mixtures were used, each acid being combined with every other. Furthermore, a progressive series was arranged, one acid at a time being added to the previous mixture, until all 14 had been introduced.

The Growth Factor. Arginine was a good acid for growth, while signs of differentiation were very meagre in the arginine groups. Cystine proved to be a very good growth factor, closely following arginine. Phenyl-arginine acted very favorably on growth, especially when combined with another acid suitable for maintenance or growth. In combination with arginine or cystine, phenyl-alanine acted particularly well. Lysine also favored growth, histidine hardly so.