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Monodehydroascorbic Acid-Transhydrogenase Activity and Coenzyme Concentrations in Tissues of Ascorbic Acid-deficient and Control Guinea Pigs¹

Department of Food and Nutrition, Cornell University, Ithaca, New York

Adrenal gland and maternal placental tissue were assayed for NADH-monodehydroascorbic acid-transhydrogenase activity in a basic system containing ascorbic acid, NADH, KCN and microsomal protein in phosphate buffer, pH 7.4. Enzyme activity was not detectable when reduced glutathione and NADPH were substituted for ascorbic acid and NADH, respectively. The reaction was inhibited by p-chloromercuribenzoate. The average rate of NADH oxidation was higher in the adrenal gland than in the maternal placenta. Enzyme activity decreased as ascorbic acid concentration was decreased. NAD⁺ and NADH concentrations were determined using an enzymatic method in adrenal glands of young male animals on ascorbic acid-deficient diets for 20 days, and in adrenal gland and maternal placenta of females on ascorbic acid-deficient diets for 15 days. Total NAD⁺ and NADH concentrations were similar in ascorbic acid-deficient and control tissues whereas the average ratio of NAD⁺/NADH was significantly depressed in the ascorbic acid-deficient tissues. The depressed ratio was attributed to a higher NADH concentration and generally lower NAD⁺ concentration than was found in control tissues. Possible relationships of depressed NAD⁺/NADH ratio and NADH-monodehydroascorbic acid-transhydrogenase activity are discussed in relation to known abnormalities of scurvy.

² This paper is part of a thesis presented to the Graduate School of Cornell University in partial fulfillment of the requirements for the Ph.D. degree. An abstract of part of this work was given at the 51st Annual Meeting of the Federation of American Societies for Experimental Biology, April 1967 (Federation Proc., 26: 280).

Manuscript received 14 August 1968.