Purification and properties of the sulfur oxygenase/reductase from the acidothermophilic archaeon, Acidianus strain S5

The sulfur oxygenase/reductase (SOR) of Acidianus strain S5 was purified and characterized after expressing the SOR gene in a recombinant strain of Escherichia coli. The N-terminal sequence of the purified SOR protein was the same as the deduced amino acid sequence from previously cloned SOR genes. Enzymatic studies indicated that the SOR catalyzed the conversion of elemental sulfur (SO) to sulfite, thiosulfate, and sulfide. The optimal pH and temperature were 5.0 and 70 degreesC, respectively. Comparison of this SOR and that of A. ambivalens revealed several differences between these two SORs. The most striking difference is that the SOR of Acidianus S5 had maximal activity at acidic pH. By application of anti-SOR serum and the Western blot technique, it was found that SOR proteins existed in A. brierleyi and in Acidianus S5 cells cultivated with thiosulfate as the sole energy source, indicating that SOR may also play a role in thiosulfate metabolism.