Purification and Properties of Membrane - bound Sulfite Dehydrogenase from thiooxldans JCM 7814 Thiobaeutus

with n-heptyl-fi-D-thioglucoside, and then purified by DEAE-Sepharose and hydroxylapatite columns containing Triton X-100. The puTified 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 optima] temperature of the membrane fraction was 25eC, while that of the purified enzyme was 20eC. The optimal pHs of both the enzymes were 7.5. The IC,,'s for sulfite of the membrane fraction and the purified enzyme were 4.88 mM and 1.95 mM, respectiyely. The actiyities of both the enzymes were increased by adding Triton X-leO and inhibited by sulfhydryl-binding reagents.