D. A. Benton

L-Leucine, an isoleucine antagonist in the rat.

Abstract An excess of dietary l -leucine has been shown to retard the growth of rats fed low-protein diets or diets deficient in isoleucine. The addition of isoleucine to such diets overcame, to a large extent, the growth-retarding action of an excess of l -leucine. These observations suggest that an excess of dietary l -leucine can act as an antimetabolite of isoleucine in the rat and can thereby increase the requirement of the rat for isoleucine.

Leucine, isoleucine and valine relationships in the rat.

Abstract Previous work had demonstrated that leucine fed to rats increased the requirement for isoleucine but, when 3% of l -leucine was fed, isoleucine only partially overcame the growth depression. It has now been shown that a supplement of valine was necessary to restore the rate of growth. Valine, isoleucine, and phenylalanine have been shown to reduce the utilization of leucine for the growth of rats fed a 9% casein diet supplemented with a number of amino acids. By using this diet and varying the levels of leucine, valine, isoleucine, and phenylalanine, evidence has been obtained for antagonisms between isoleucine and valine, between phenylalanine and isoleucine, and between phenylalanine and valine. It is suggested that antagonisms between each of these pairs of amino acids may be found under the proper dietary conditions.

Effect of isoleucine supplementation on the growth of rats fed zein or corn diets.

Abstract Isoleucine was found to be limiting for the growth of rats fed corn diets supplemented with lysine, tryptophan, valine, and threonine or 24% zein diets supplemented with most of the essential amino acids. Since phenylalanine, which is known to be present in zein at quite a high level, was also found to be limiting for the growth of rats fed 21% of zein, it was suggested that all of the essential amino acids in zein were utilized poorly. This was further substantiated when rats fed diets containing alcohol-extracted corn showed a much greater growth response to a level of isoleucine equivalent to that supplied by the zein extracted than to the zein itself. When the level of leucine supplied by the zein was also added, no growth depression was obtained.

Phenylalanine as an amino acid antagonist for the rat

Abstract The growth rates of rats fed a 9% casein diet supplemented with tryptophan and methionine were markedly depressed by supplements of either 3% of dl -phenylalanine or 3% of l -tyrosine. A supplement of threonine prevented this effect in both cases. Threonine was only partly effective against the more severe growth depression caused by 5% of dl -phenylalanine. Threonine did not prevent the growth depression caused by phenylalanine when tryptophan was not added to the diet. Phenylalanine reduced the level of liver fat under the conditions studied. A comparison is made with the leucine-isoleucine antagonism and possible mechanisms are discussed.

Effect of partial deficiency of threonine on enzyme activity and fat deposition in liver.

Summary The effect of a partial deficiency of threonine in the rat on the activities of several liver enzymes and on liver fat deposition has been determined. Liver fat deposition, in confirmation of earlier reports, was higher in animals receiving the threonine-deficient diet. The activities of the mitochondrial enzymes, succinic oxidase and choline oxidase, were higher in liver homogenates from threonine-deficient animals. Endogenous respiration and the activities of the cytoplasmic enzymes, xanthine oxidase and tyrosine oxidase, were lower in the livers of animals fed diets deficient in threonine.

Properties of substances in gelatin which stimulate the growth of chicks fed amino acid diets.

Abstract Fractionations of an acid hydrolyzate of gelatin were carried out and the fractions assayed for growth-stimulating activity with chicks fed amino acid diets. The growth-stimulating activity was not extracted with n -butanol; was partly extracted with phenol; was not precipitated by basic lead acetate or phosphotungstic acid; was not taken up by Amberlite IR4B; but was taken up by Dowex 50 and eluted with acid. The properties of the active materials are discussed.

Effect of different dietary fats on choline requirement of rats.

Summary 1. Rats fed on diet containing butter fat required a higher level of choline to reduce the level of liver fat to within the normal range, than did rats fed the same level of corn oil. This “requirement” for choline, as measured by liver fat, was not greater than 0.12% of choline chloride with diet containing 30% of corn oil and about 0.15% of choline chloride with diet containing 30% of butter fat. These values were not affected by supplements of cystine, or methionine and tryptophan or all 3 amino acids. 2. When no choline was fed, rats receiving butter fat grew at a more rapid rate than those receiving corn oil. It is suggested that the reduced rate of growth of rats fed corn oil was caused by kidney damage.