The quality of proteins.

Dr. D. P. Cuthbertson (Rowett Research Institute, Bucksburn, Aberdeen) It is the amino-acid composition of the proteins in relation to the needs of the organism at the moment which is our main concern, but before I pass to the main topic of our discussion I would remind you that it is the physico-chemical character of the proteins of wheat 0 0 ~ which governs the texture of bread, the caseinogen of milk, its curd, and the coaguhtive properties of native proteins, the vast array of appetizing egg dishes. Historim1 The pioneer experiments of Willcock and Hopkins (1906-07) and of Osborne and Mendel (1914) on the effect on growth of proteins lacking certain amino-acids were subsequently brought to a new stage when Rose, one of Mendel’s most distinguished pupils, determined the amino-aoids indispensable for the growth of the rat. Rose defined an indispensable dietary component as “one which cannot be synthesized by the animal organism, out of the materials ordinarily available a t a speed commensurate with the demands for normal growth”. Almquist, Jackson, Albanese, Holt, Mitchell and their collaborators have added to this knowledge by studies on animals, including man. As Dr. C. P. Stewart will be dealing in detail with this aspect (Stewart, 1946), I will simply mention that of the amino-acids which Rose (1938) and Rose and Rice (1939) found essential for the normal growth of the rat and dog, namely, valine, methionine, histidine, lysine, tryptophane, phenylalanine, threonine, leucine, isoleucine and arginine, Rose, Haines and Johnson (1942), Rose, Haines, Johnson and Warner (1943) and Albanese, Holt, Frankston, Kajdi, Brumback and Wangerin (1943) have already demonstrated that for men all these, with the exception of histidine, appear to be essential for full functional maintenance. The transamination shuttle mechanism described by Braunstein and Kritzman (1937), and the transmethylation mechanism revealed by Du Vigneaud, Chandler, Cohn and Brown (1940) have gone far to open our eyes to the internal transmutations which may occur and which thus render many of the known amino-acids dispensable in the diet. The tissue protein synthesized during growth on the ten indispensable amino-acids must be assumed to be of a type normal and characteristic of the species, since it is considered axiomatic that “the tissues either form a typical protoplasmic product or none at all” (Osborne and Mendel, 1914). The work of Lee and Lewis (1934) and Louis and Lewis (1944) indicates that the composition of the tissue proteins is not