[An oxidation enzyme for hydrogen sulfide from Hyphomicrobium neptunium ATCC15444]

We described in our previous paper that the cell-free extract from Hyphomicrobium neptunium ATCC 15444 oxidized hydrogen sulfide to sulfur. We tried to purify the enzyme used for this oxidation to determine the molecular nature of this enzyme. The 40% ammonium sulfate precipitate from the supernatant of cell sonicate of H. neptunium was chromatographed on a column of Phenyl Sepharose CL-4B and its active fractions were collected. These fractions were further purified through Superose 12 and then TSK gel G3000SW column chromatographies. A protein of molecular weight about 54,000 and isoelectric point pI 6.8 was isolated. However, this final protein was found to reduce its activity to less than one-tenth of those of ammonium sulfate precipitate and of the fraction from Phenyl Sepharose CL-4B column chromatography. This might be caused either by the loss of accessory component or by its requirement of low molecular factors necessary for its activation at the stage of gel filtration. The neutral isoelectric point of this enzyme could be suitable as the function of H. neptunium because its final product was S0, and it grows at neutral pH. In contrast, the final oxidative product of hydrogen sulfide by Thiobascillus is sulfuric acid, and they grow at acidic pH.