THE RELATION OF LEUCINE, ISOLEUCINE, AND NORLEUCINE TO GROWTH

Abstract

Before the isolation and identification of threonine (a-amino+ hydroxy-n-butyric acid) had actually been accomplished (cf.Mc-Coy, Meyer, and Rose (1935-1936), and Meyer and Rose (1936)), several investigations, designed to determine the nutritive importance of certain recognized protein components, were already under way in this laboratory.In these studies, advantage was taken of the fact that excellent growth may be induced in rats by the administration of diets in which the nitrogen is supplied in t,he form of mixtures of the known amino acids supplemented with crude concentrates of threonine.Under such conditions, the removal from the food of an essential constituent naturally is reflected in the weight changes of the experimental animals.By the use of this procedure, phenylalanine was shown to be indispensable for life, and incapable of being replaced by tyrosine (Womack and Rose, 1934).In a similar fashion, studies have been made of the physiological r&e of leucine, isoleucine, and norleucine.The details of the methods employed and the results obtained are outlined below.