Enzymes involved in the metabolism of thiosulfate by Thiobacillus thioparus. I. Survey of enzymes and properties of sulfite : cytochrome c oxidoreductase

Abstract

Enzymes concerned with the oxidation of thiosulfate were investigated in extracts of Thiobacillus thioparus. The organism possessed sulfite oxidase as well as adenosine-5′-phosphosulfate reductase and thiosulfate-oxidizing enzyme. Sulfite oxidase was purified 160-fold and the properties were studied. The enzyme had a molecular weight of 54 000 and one non-heme iron. The pH had a marked effect on reaction velocity and K_m for sulfite, and the pK values for free enzyme and enzyme–sulfite complex were determined as 8.9 and 6.2, respectively. Chloride inhibition was noncompetitive and phosphate was uncompetitive with respect to sulfite. In many properties the T. thioparus enzyme was similar to the enzyme isolated from Thiobacillus novellus.