The Metabolism of Proteins and Amino Acids

Abstract

In the compilation of this review an attempt has been made to give appropriate recognition· to the current interest in normal and emer gency nutrition, by discussing such aspects as the amino acid needs of the human subject, the synthesis of blood proteins, intravenous ali mentation, and the use of urea by ruminants. References to papers in the fields of plant and bacterial metabolism have been largely omitted. During the year many delayed foreign journals have become available, but their arrival has been erratic and it has not been possible to fill some of the gaps. Throughout the review 1 and d have been used in the configurational sense.Essential amino acids.-The amino acid requirements for main tenance in the adult human subject have recently been tested with protein hydrolyzates and with mixtures of purified amino acids as the chief or sole source of protein nitrogen. Studies of the former type have come chiefly from the laboratory of Holt. Nitrogen equilibrium was readily maintained on an enzymic hydrolyzate of casein, but this was not possible with acid-hydrolyzed casein until tryptophan . �had been added (1, 2). Two other acid hydrolyzates were prepared, one from casein which had been deaminized to destroy the lysine (3) and the other from casein which had been oxidized with hydrogen perox ide (4, 5) to convert the methionine to the corresponding biologically inactive sulfone (6) which was removed as the insoluble calcium sul fonate. From the latter preparation most of the residual cystine was also removed by adsorption on norit. When the former hydrolyzate was fed in diets fortified with tryptophane, equilibrium was not at tained until lysine was added (7, 8). Supplementation of the latter hydrolyzate with tryptophane, methionine, and cystine provided a mix ture adequate for maintenance. Removal of the methionine produced negative nitrogen balances and loss of body weight; its restoration re-established nitrogen equilibrium in a few days, but did not increase the body weight. 0 The inconsistent results obtained by the omission of cystine were considered to suggest that cystine was essential, but this conclusion was t.bought to require confirmation (9). An abstract 239 Annu. Rev. Biochem. 1944.13:239-262. Downloaded from www.annualreviews.org Access provided by Technische Universiteit Eindhoven on 02/02/15. For personal use only.Quick links to online content Further ANNUAL REVIEWS

A COMPARISON OF d AND l‐TRYPTOPHAN ON THE CEREBRAL METABOLISM OF 5‐HYDROXYTRYPTAMINE AND DOPAMINE IN THE DOG

“…Numerous studies (du Vigneaud, Sealock & Van Etten, 1932;Berg, 1934;Oesterling & Rose, 1952) have shown that the rat is able to use D-tryptophan almost as well as L-tryptophan for growth, which is consistent with Yuwiler's explanation of increased formation of 5-hydroxyindoles from D-tryptophan. There is a likelihood of human exposure to Dtryptophan because it is sweet (Berg, 1942;Berg, 1953). It could then be considered as a substitute for the currently used artificial sweetener Saccharin, cyclamate already having been withdrawn for toxicological reasons.…”