Substrate Phosphorylation in Chlorobium vibrioforme f. sp. thiosulfatophilum

Summary: Chlorobium vibrioforme f. sp. thiosulfatophilum was shown to oxidize sulphate via substrate phosphorylation involving adenylylsulphate (APS) reductase, ADP-sulphurylase and adenylate kinase. APS reductase was purified 200-fold and shown to be a flavoprotein of molecular weight 1.8 × 105, containing 1 mol flavin adenine dinucleotide (FAD), 4-6 mol non-haem iron and 6-8 mol labile sulphide (mol enzyme)-1. Substrate inhibition of the enzyme was observed when the AMP concentration was above 2 mM. ADP-sulphurylase purified free of adenylate kinase had an apparent K m value for APS of 0.25 mM, which increased with decreasing concentrations of phosphate.