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The recently described extremely thermophilic sulphate-reducing archaebacterium ‘VC-16’ has been shown to contain adenylylsulphate reductase (EC 1.8.99.2). The enzyme was purified 26-fold by ammonium sulphate fractionation, DEAE-cellulose chromatography, hydrophobic chromatography and preparative isoelectric focusing. The enzyme preparation gave a single band on analysis by SDS-PAGE. The M r was 160000 and the enzyme contained 1 mol FAD, 8 mols non-haem iron and 6 mols labile sulphide per mol enzyme. Ferricyanide was used as electron acceptor. The optimal reaction temperature was 85 °C under the assay conditions used and the pH optimum of the enzyme reaction was 8·0. The K m values for AMP and ferricyanide were 1 mm and 0·4 mm, respectively. The p1 of the archaebacterial adenylylsulphate reductase was 4·8.
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