SummaryTwo different pathways for thiosulphate oxidation are present in the purple sulphur bacterium Allochromatium vinosum: oxidation to tetrathionate and complete oxidation to sulphate with obligatory formation of sulphur globules as intermediates. The tetrathionate:sulphate ratio is strongly pH-dependent with tetrathionate formation being preferred under acidic conditions. Thiosulphate dehydrogenase, a constitutively expressed monomeric 30 kDa c-type cytochrome with a pH optimum at pH 4.2 catalyses tetrathionate formation. A periplasmic thiosulphateoxidizing multienzyme complex (Sox) has been described to be responsible for formation of sulphate from thiosulphate in chemotrophic and phototrophic sulphur oxidizers that do not form sulphur deposits. In the sulphur-storing A. vinosum we identified five sox genes in two independent loci (soxBXA and soxYZ). For SoxA a thiosulphate-dependent induction of expression, above a low constitutive level, was observed. Three sox-encoded proteins were purified: the heterodimeric c-type cytochrome SoxXA, the monomeric SoxB and the heterodimeric SoxYZ. Gene inactivation and complementation experiments proved these proteins to be indispensable for thiosulphate oxidation to sulphate. The intermediary formation of sulphur globules in A. vinosum appears to be related to the lack of soxCD genes, the products of which are proposed to oxidize SoxY-bound sulphane sulphur. In their absence the latter is instead transferred to growing sulphur globules.

In the hyperthermophilic sulfate reducer Archaeoglobus fulgidus DSM 4304 , two open reading frames (sat and ORF2) are located upstream of the aprBA genes encoding adenosine-5P-phosphosulfate (APS) reductase. sat-ORF2-aprBA probably form a transcriptional unit, since sat is preceded by putative promoter sequences and termination signals are found downstream of aprA. While the 117-residue ORF2 product does not show significant similarity to known proteins, the 456-residue, 52.78-kDa, sat-encoded polypeptide exhibits similarity to the homo-oligomeric adenosine triphosphate (ATP) sulfurylases from sulfuroxidizing bacteria and from sulfate-assimilating bacteria and eukaryotes. Functional overexpression of sat in Escherichia coli proved that the encoded protein acts as an ATP sulfurylase. The recombinant protein was purified to homogeneity and found to be a homo-dimer. Comparison of sulfate and thiosulfate grown A. fulgidus revealed that ATP sulfurylase and APS reductase are constitutive enzymes. Distance matrix analyses allowed insights into the evolution of prokaryotic ATP sulfurylases. z 1998 Published by Elsevier Science B.V.

In the hyperthermophilic sulfate reducer Archaeoglobus fulgidus DSM 4304T, two open reading frames (sat and ORF2) are located upstream of the aprBA genes encoding adenosine-5'-phosphosulfate (APS) reductase. sat-ORF2-aprBA probably form a transcriptional unit, since sat is preceded by putative promoter sequences and termination signals are found downstream of aprA. While the 117-residue ORF2 product does not show significant similarity to known proteins, the 456-residue, 52.78-kDa, sat-encoded polypeptide exhibits similarity to the homo-oligomeric adenosine triphosphate (ATP) sulfurylases from sulfur-oxidizing bacteria and from sulfate-assimilating bacteria and eukaryotes. Functional overexpression of sat in Escherichia coli proved that the encoded protein acts as an ATP sulfurylase. The recombinant protein was purified to homogeneity and found to be a homo-dimer. Comparison of sulfate and thiosulfate grown A. fulgidus revealed that ATP sulfurylase and APS reductase are constitutive enzymes. Distance matrix analyses allowed insights into the evolution of prokaryotic ATP sulfurylases.

No abstract