Amino Acid Balance and Imbalance

The question of the specificity of the second most limiting amino acids, methionine and phenylalanine, in causing an imbalance in diets containing 6% of fibrin has been examined. A variety of amino acids and combinations of amino acids caused growth depressions under the conditions of these experiments. Among the growth depressions, that caused by leucine has been attributed to the antagonism between it and isoleucine and valine. Addition of leucine to the diet reduces the efficiency of utilization of isoleucine, valine and histidine. Additions of certain combinations of the least limiting amino acids, arginine, threonine and tryptophan also caused growth depressions of the same magnitude as that caused by the addition of methionine and phenylalanine.