Species specific release of sulfate from adenylyl sulfate by ATP sulfurylase or ADP sulfurylase in the green sulfur bacteria Chlorobium limicola and Chlorobium vibrioforme

High activities of ATP sulfurylase were found in the soluble protein fraction of two Chlorobium limicola strains, whereas ADP sulfurylase was absent. ATP sulfurylase was partially purified and characterized. It was a stable soluble enzyme with a molecular weight of 230,000, buffer-dependent pH optima at 8.6 and 7.2 and an isoelectric point at pH 4.8. No physiological inhibitor was found. Inhibition was observed with p-CMB and heavy metals. Sulfur compounds had no effect on enzyme activity. The stoichiometry of the reaction was proven. In contrast, an ADP sulfurylase, but no ATP sulfurylase, was found in Chlorobium vibrioforme. This enzyme was very labile with a molecular weight of about 120,000 and buffer-dependent pH optima at 9.0 and 8.5. Under test conditions the apparent K _m value was determined to be 0.28 mM for adenylyl sulfate and 8.0 mM for phosphate.Abbreviations APS adenylyl sulfate - p-CMB parachloromercuribenzoate - PP_i inorganic pyrophosphate