Formate Oxidation by Particulate Preparations from Higher Plants

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Abstract
Washed cyto-plasmic particles were prepared from sucrose solution homogenates by differential centrifugation. The oxidation of formate-C14 was measured by the amount of C14O2 formed. Cabbage, pea, spinach, radish, cauliflower, turnip, and squash showed a formic dehydrogenase activity which was localized almost completely in the particulate fraction. The characteristics of the reaction were studied with cabbage particles. Added diphosphopyridine nucleotide (DPN) only gave a slight stimulation to the oxidation by the particles. The enzyme could be solubilized by a digitonin or acetone treatment. Under these conditions DPN stimulation was very large. Triphosphopyridine nucleotide could not substitute for DPN. The oxidation by the particles was inhibited almost completely by 10-3 M KCN or sodium azide. The addition of of 5 x 10-3 M adenine nucleotides also was inhibitory. Phosphoenol-pyruvate and 3-phosphoglyceric acid at a final concentration of 10-3 M inhibited 80 and 65% respectively. Pyruvate did not have any effect. A Lineweaver-Burk plot gave a Ks of 5 x 10-3 M.