J. N. Williams

Evaluation of the Sakaguchi Reaction for Quantitative Determination of Arginine.

Summary The Sakaguchi reaction has been studied to obtain a reliable quantitative method for the colorimetric estimation of arginine. The best conditions for this method have been investigated and reported. The method has been found to be entirely satisfactory for determining arginine over the range of 0-30 γ. Duplicability of the method is ± 0.5%, (Standard deviation).

Effect of methionine deficiency upon enzyme activity in the rat.

Summary It has been observed that a methionine deficiency in the rat reduces liver succinic dehydrogenase activity slightly, completely reduces liver xanthine oxidase activity, and has practically no effect upon endogenous respiration of liver tissue in vitro.

New procedure for ascorbic acid analysis by the osazone method.

Summary The osazone method for ascorbic analysis(l) and a number of published modifications of this method (2-4) have been evaluated to derive a procedure which is simultaneously sensitive, specific, accurate, and easy to carry out for routine analyses. In the resulting method, the time-consuming use of Norit and 85% sulfuric acid(l) is avoided, the sensitivity is twice that obtained when glacial acetic acid (3) is used, and a source of error introduced with the use of 2,6-dichloro-phenolindophenol(4) to oxidize ascorbic acid before formation of the osazone is eliminated. The resulting method has been found to be quite satisfactory with respect to sensitivity, specificity, facility, and recovery of added ascorbic acid.

Response of Liver Enzymes and Other Proteins to Amino Acid Deficient Diets.

Summary 1. Histidine-deficient diet can completely restore xanthine oxidase activity to livers of rats previously depleted of such activity by a non-protein diet; methionine-free and lysine-free diets partially restore such activity with the lysine-free diet the least active in this respect. 2. Liver succinic oxidase activity can be similarly restored by histidine-and methionine-free rations but only partially restored by a lysine-free ration. 3. Liver choline oxidase activity of protein-depleted rats can be restored partially and to about the same extent by the 3 amino acid-deficient diets studied. 4. Liver nitrogen concentration follows approximately the same pattern as succinic oxidase in these studies. 5. The enzymatic responses to a non-protein diet followed by single amino acid-deficient diets have been compared to responses observed in earlier studies under conditions of initial single amino acid-deficient diets.

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.

Colorimetric method for rapid determination of arginase activity.

Summary A method has been presented for the rapid determination of arginase with a minimum of operations and equipment. The activity of as low as 20 γ of whole liver can be determined. The arginine remaining after enzymatic hydrolysis is estimated by a quantitative modification(9) of the Sakaguchi reaction. Additional studies are presented indicating the necessary substrate concentration, the pH optimum, and linearity of the enzyme concentration curve for these experimental conditions.

Interrelationships of Vitamin B6, Niacin, and Tryptophan in Pyridine Nucleotide Formation.∗

Summary 1. It has been observed that a pyridoxine deficiency in the rat does not disturb the normal conversion of tryptophan to liver pyridine nucleotides to any demonstrable extent. 2. Niacin fed to pyridoxine-deficient rats spares liver pyridine nucleotide concentrations. 3. Tryptophan fed in excess along with normal dietary protein in a complete ration increases liver pyridine nucleotides concentrations above normal demonstrating that the excess metabolite can be utilized rather than simply degraded and excreted.

Comparative Effect of Tryptophan, Niacin, and Nicotinamide in Forming Liver Pyridine Nucleotides.∗

Summary Changes in the level of liver pyridine nucleotides (PN) of rats were studied at various times following the administration by stomach tube of equimolar amounts of tryptophan, niacin, or niacinamide. Tryptophan was observed to be equally effective as a PN precursor as equimolar amounts of niacin, whereas niacinamide produced significantly higher levels of liver PN than either tryptophan or niacin. When incorporated directly into the ration, however, niacin and tryptophan were again equivalent as PN precursors whereas, under these conditions, nia-cianamide was a slightly less efficient PN precursor than niacin or tryptophan.

Effect of Aminopterin on Choline, Betaine Aldehyde, and Betaine Metabolism.

Summary 1. The effects of dietary amino-pterin upon the aerobic and anaerobic metabolism of choline, betaine aldehyde, and betaine have been investigated. 2. Oxidation of choline and betaine aldehyde, anaerobic conversion of betaine aldehyde to betaine, and both aerobic and anaerobic transmethylation to homocysteine are decreased significantly by dietary aminopterin.

The Mechanisms of the Choline Oxidase and Transmethylase Enzyme Systems.

Summary (1) The mechanism of choline and betaine aldehyde conversion to betaine and methyl group transfer to homocysteine have been investigated both in aerobic and anaerobic systems. (2) The expected yield of acid groups, assumed to be betaine, from oxidation of choline and betaine aldehyde is only one-half the theoretical. (3) Betaine aldehyde appears to be metabolized by 2 pathways, one an aerobic oxidation and the other an anaerobic conversion to betaine. (4) Choline, betaine aldehyde, and betaine are equivalent methyl group donors to homocysteine under aerobic conditions. Anaerobically choline is almost inactive in furnishing methyl groups to homocysteine. Betaine, however, is a more active methyl donor anaerobically than under aerobic conditions.