The citric acid cycle

Abstract

ALTHOUGH, in the view of the author, the preceding paper [Krebs & Eggleston, 1940] removes any doubt about the occurrence and significance of the citric acid cycle in pigeon breast muscle, it was thought desirable to clarify the situation, by discussing in full some of the criticisms of the theory which Breusch [1937; 1939] and Thomas [1939] have expressed in recent papers. Both authors admit the occurrence of the citric acid cycle, but believe it to be an unimportant side reaction. Breusch argued that citrate was formed only in experiments in which the concentration of oxaloacetate was unphysiologically high and that the citrate was not formed from oxaloacetate, but from some undefined impurity. The latter argument was based on the fact that the yield of citrate in his experi- ments never exceeded 2 % of the oxaloacetate added. Thomas [1939] observed that under certain conditions 100 mg. of added oxaloacetate yielded 16-22 mg. malate and only 1-3-1*8 mg. citrate. Breusch [1939] published at the same time