Studies on an Enzyme System from Wheat Germ Catalyzing the Aerobic Oxidation of Reduced Triphosphopyridine Nucleotide.

Abstract

Crude "malic" enzyme preparations from wheat germ were found to contain enzymes catalyzing the aerobic oxidation of reduced triphosphopyridine nucleotide (TPNH). With malate as the substrate these enzyme preparations catalyze the following reactions A. malate + TPN+[forward arrow] pyruvate + CO2+TPNH+H+. B. TPNH + H+ + 1/2 O2[forward arrow]TPN+ + H2O. Evidence is presented for a cofactor and Mn++ requirement for full activity of the oxidase system catalyzing reaction B. The cofactor, as yet unidentified, has been found in yeast glutathione preparations and in crude coenzyme A preparations from liver. The cofactor, however, is neither glutathione nor coenzyme A. Evidence is presented that the cofactor exists in both the oxidized and reduced form; the oxidized form being the active one. The requirement of the oxidase system for Mn++ is quite specific. Neither Co++ or Mg++ can substitute for Mn++.