ATP SULFURYLASES FROM SULFATE-REDUCING BACTERIA OF THE GENUS DESULFOVIBRIO - A NOVEL METALLOPROTEIN CONTAINING COBALT AND ZINC

Adenosine triphosphate sulfurylase catalyzes the formation of adenosin e 5'-phosphosulfate from adenosine triphosphate and sulfate. The enzym e plays a crucial role in sulfate activation, the key step for sulfate utilization, and has been purified from crude extracts of Desulfovibr io desulfuricans ATCC 27774 and Desulfovibrio gigas. Both proteins are homotrimers [141 kDa (3 x 47) for D. desulfuricans and 147 kDa (3 x 4 9) for D. gigas] and have been identified, for the first time, as meta lloproteins containing cobalt and zinc. EXAFS reveals that either coba lt or zinc binds endogenously at presumably equivalent metal binding s ites and is tetrahedrally coordinated to one nitrogen and three sulfur atoms. Furthermore, the electronic absorption spectra display charge- transfer bands at 335 and 370 nm consistent with sulfur coordination t o cobalt, and as expected for a distorted tetrahedral cobalt geometry, d-d bands are observed at 625, 666, and 715 nm. This geometry is supp orted by the observation of high-spin Co2+ EPR signals at g approximat e to 6.5.