The sulfite-activated oxidation of reduced pyridine nucleotides by peroxidase

Abstract

1. 1. The aerobic oxidation of sulfite ions is initiated by peroxidase in the presence of Mn ++ or certain phenolic compounds such as thyroxine or estradiol. An inhibition of sulfite oxidation by the peroxidase-thyroxine-O 2 system was produced by epinephrine, glutathione, sodium thiosulfate, ascorbic acid, catalase and reduced diphosphopyridine nucleotide. 2. 2. The oxidation of reduced diphosphopyridine nucleotide (or reduced triphosphopyridine nucleotide) by horseradish peroxidase, Mn ++ and oxygen is stimulated by sulfite ions. Hemoglobin, myoglobin, myeloperoxidase, a uterine homogenate and relatively large concentrations of inorganic iron can replace horseradish peroxidase in this reaction. Sulfite was most effective when cacodylate, phosphate, and to a lesser extent, arsenate buffers were employed, and was less effective in the presence of Tris, glycylglycine, or imidazole buffers at pH 7.0. The sulfite-activated oxidation of reduced diphosphopyridine nucleotide was inhibited by copper, hydrogen peroxide, sodium thiosulfate, glutathione, epinephrine, and ascorbic acid. 3. 3. Sulfite and thyroxine, or sulfite and estradiol have a synergistic effect on the oxidation of reduced diphosphopyridine nucleotide by the Mn ++-peroxidase-O 2 system. Sulfite ions have been employed in this way to magnify the response of the uterine enzyme to thyroxine and estradiol.