Studies on the metabolism of a sulfur-oxidizing bacterium VI. Fractionation and reconstitution of the elementary sulfur-oxidizing system of Thiobacillus thiooxidans

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The sulfur-oxidizing system of a strain of Thiobacillus thiooxidans was obtained in cell-free state. The system is resolved into three fractions and can be reconstituted from these fractions. Both the soluble and particulate fractions are required for the oxidation of elementary sulfur. The soluble fraction was further separated into two fractions, the collodion membrane-permeable(S-P) and the impermeable(S-IP). S-P contains a low molecular weight, relatively heat stable substance(s) which is indispensable for the reconstitution of the sulfur-oxidizing system and was identified as a pyridine nucleotide. The function of S-P can be replaced by NAD or NADP, but not by cysteine nor GSH. Oxidation of NADH_2 and NADPH_2 is catalyzed by the particulate fraction. Oxidation of the latter is much more rapid than that of the former. Oxidation of NADPH_2 as well as sulfur oxidation is inhibited by cyanide, pCMB and CO, the CO-inhibition being photo-irreversible. However, strong inhibitors of sulfur oxidation such as DDC, 8-hydroxyquinoline and salicylaldoxime have no effect on the oxidation of NADPH_2. The optimum pH values for sulfur and sulfite oxidations by the cell-free extract are shifted to the neutral side in comparison with pH values by intact cells.
日本植物生理学会の論文