The oxidation of malic and mesotartaric acids in pigeon-liver extracts

Abstract

A fraction of pigeon liver was obtained which oxidized sodium DL-malate anaerobically in the presence of ferricyanide and without added diphosphopyridine nucleotide (DPN), tri-phosphopyridine nucleotide (TPN) or manganous ions. The Km value was 6.2 x 10-3 [image] for DL-malate, 3.1 x 10-3 [image] for L-malate. Tartronic acid, maleate, isocitrate, malonate, citrate gave strong inhibition but butyrate, beta-hydroxybutyrate and gluconate had no effect. D-tartrate and DL-tartrate did not inhibit but meso-tartrate was a competitive inhibitor. In the presence of DPN or TPN, the pigeon liver-ferricyanide system oxidized mesotartaric acid with a high Km value, 1.4 x 10-2 [image]. This was not inhibited by the above inhibitors for malate oxidation. The fact that DPN, TPN or Mn++ are not required, the Km value and the marked inhibition by various carboxylic acids distinguishes this oxidation of malate from that of L-malic dehydrogenase of pig-heart and Escherichia coli.