Purification and Properties of Membrane-bound Sulfite Dehydrogenase from Thiobacillus thiooxidans JCM7814

Abstract

Sulfite dehydrogenase in the membrane fraction of Thiobacillus thiooxidans JCM7814 was solubilized with n-heptyl-β-D-thioglucoside, and then purified by DEAE-Sepharose and hydroxylapatite columns containing Triton X-100. The purified enzyme was electrophoretically homogeneous. The enzyme had an apparent molecular mass of 400kDa, and was composed of three subunits whose molecular masses were 74, 70, and 62 kDa. The purified enzyme was much more labile than the membrane-bound enzyme (membrane fraction). The optimal temperature of the membrane fraction was 25°C, while that of the purified enzyme was 20°C. The optimal pHs of both the enzymes were 7.5. The K_m's for sulfite of the membrane fraction and the purified enzyme were 4. 88 mM and 1.95 mM, respectively. The activities of both the enzymes were increased by adding Triton X-100 and inhibited by sulfhydryl-binding reagents.