THE INFLUENCE OF THE TYPE OF CARBOHYDRATE INGESTED UPON CITRIC ACID PRODUCTION* BY CURTIS E. MEYERt AND ARTHUR

The “citric acid cycle” hypothesis of carbohydrate oxidation has stimulated an interest in the general relationship of citric acid to carbohydrate metabolism. Krebs and Johnson (1937, a) and Krebs (1937) have presented evidence which they believe demonstrates that a catalytic system composed of certain dicarboxylic acids and citric acid “outlines the principal pathway of the oxidative breakdown of carbohydrate in muscle tissue.” According to their scheme, an increased rate of oxidation of carbohydrate would result in the elaboration of more citric acid. A precursor of the citric acid thus formed might be any other member of the cycle. Krebs and Johnson (1937, 6) showed that succinic acid may bc synthesized in small amounts by animal tissue in vitro if pyruvic acid is available. On the basis of this observation these authors infer t,hat the origin of citric acid is explained. Although Greenwald (1914) showed that citric acid is practically quantitatively converted to glucose in the human diabetic and in phlorhizinized dogs, definite evidence that the reverse reaction occurs in animals is lacking. The ingestion of glucose has been reported to have no effect in human beings either on the excretion of citric acid (Kuyper and Mattill, 1933) or on its concentration in the blood (Len&r, 1934). Sherman, Mendel, and Smith (1936) were unable to obtain convincing evidence that