Adenylylsulfate reductases from archaea and bacteria are 1:1 αβ‐heterodimeric iron–sulfur flavoenzymes – high similarity of molecular properties emphasizes their central role in sulfur metabolism

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Abstract
Highly active adenylylsulfate (APS) reductase was isolated under N2/H2 from sulfate‐reducing and sulfide‐oxidizing bacteria and archaea. It was a 1:1 αβ‐heterodimer of molecular mass ≈95 kDa, and two subunits (α≈75, β≈20 kDa). The specific activity was 11–14 μmol (min mg)−1; cofactor analysis revealed 0.96±0.05 FAD, 7.5±0.1 Fe and 7.9±0.25 S2−. The photochemically reduced enzyme had a multiline EPR spectrum resulting from two interacting [4Fe–4S] centers. The properties of the different APS reductases were remarkably similar, although the enzyme is involved in different metabolic pathways and was isolated from phylogenetically far separated organisms. A structural model is proposed, with FAD bound to the α‐subunit, and two [4Fe–4S] centers located in close proximity on the β‐subunit.

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