[Oxidation of hydrogen sulfide with cell-free extract of Hyphomicrobium neptunium ATCC 15444].

Soluble (Fr. 1) and membrane (Fr. 2) fractions were prepared from the cell-free extract of Hyphomicrobium neptunium ATCC 15444, and their effects on the oxidization of hydrogen sulfide (H2S) were studied. When H2S gas was supplied to Fr. 1 and Fr. 2, sulfur in both fractions and the majority of thiosulfate ion in Fr. 1 were detected. The sulfide-oxidizing activity in Fr. 2 but not in Fr. 1 was inhibited by the addition of diethyldithiocarbamate, suggesting that Fr. 1 and Fr. 2 have different types of sulfide-oxidase, and that Fr. 2 would include cytochrome c dependent sulfide oxidase. It was also found that thiosulfate ion was formed from sulfur and sulfite ion by adding Fr. 1. However, the pronase-treatment of Fr. 1 did not influence on the formation of thiosulfate ion. These results suggest that H2S was oxidized to sulfur and sulfite ion by two types of sulfide oxidase and sulfur oxidase in H. neptunium ATCC 15444, and that the sulfite ion changed rapidly to thiosulfate through a non-enzymatic reaction with sulfur.