Some properties of the malic enzyme of pigeon liver. 2. Synthesis of malate from pyruvate

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Abstract
The synthesis of malate from pyruvate and bicarbonate by the malic enzyme of pigeon liver has been studied. Malate synthesis was inhibited by CO2 when the CO2 pressure was above about 0.45 atmosphere. The apparent Michaelis constant for pyruvate was very high. Bivalent metal ions were essential for the reaction. The same rate was given by 0.033 m[image] Mn++ as by 3:3 m[image] Mg++ or Co++. Zn++ and Cu++ were inhibitory. In the presence of 10 m[image] pyruvate, 40-50% inhibition was caused by tartronate (0.1-0.01 m[image]), fluorocitrate (0.1 m[image]), malonate (m[image]), L-malate (m[image]), oxaloacetate (1-10 m[image]), D- and L-lactate, DL-[alpha]-hydroxybutyrate and mesoxalate (all 20 m[image]). mesoTartrate and citrate were weaker inhibitors. Propionate and DL-[beta]-hydroxybutyrate were not inhibitory. Triphosphopyridine nucleotide which had been reduced by dithionite was non-enzymically oxidized in the presence of Mn++, CO++, Ni++ or Cu++. Enzymically reduced triphosphopyridine nucleotide did not show this phenomenon unless sulfite was added. The oxidation in the presence of Cu++ was inhibited by bicarbonate; that by the other ions was increased by bicarbonate.