The citric acid cycle and the Szent-Györgyi cycle in pigeon breast muscle

IT is known from Szent-Gy6rgyi's work [1935; 1936] that oxaloacetate can be reduced by muscle tissue to form a mixture of fumarate and 1(-)-malate.Szent-Gyorgyi formulates this reaction as follows:+ "hydrogen of the fubstrates fumarate + (1) Oxaloacetate 1ubstraeslate So far two reactions which amplify the term "hydrogen of the substrates" have been described, viz.: (2) " Triose " + oxaloacetate-pyruvate + J fumarate + [Szent-Gyorgyi, 1936; Parnas & 4 I( -)-malate Szankowski, 1937] and 0 (3) Oxaloacetate + + oxaloacetate -_*citrate +C02+ t( f )malrate [Johnson 1937]In this paper is described a third reaction in which oxaloacetate is reduced:(4) Citrate + oxaloacetate -a oc-ketoglutarate + C02 + fumarate 9