NONRADIOACTIVE ADENOSINE 5'-PHOSPHOSULFATE SULFOTRANSFERASE ASSAY BY COUPLING WITH SULFITE REDUCTASE AND O-ACETYLSERINE(THIOL)LYASE

Adenosine 5'-phosphosulfate (APS) sulfotransferase is thought to be an enzyme that transfers the sulfo-group of APS to a carrier compound wi th a thiol group in the assimilatory sulfate reduction pathway of high er plants. We developed a rapid, non-radioactive assay for APS sulfotr ansferase. Sulfite released by APS sulfotransferase reaction in the pr esence of excess dithiothreitol was further converted to cysteine by c oupling with yeast sulfite reductase and cabbage O-acetylserine(thiol) lyase. The cysteine thus formed was measured colorimetrically. By this method, 5 to 300 nmol of sulfite could be assessed. When the method w as applied to APS sulfotransferase, the enzyme activity was APS-depend ent with the partially purified enzyme. We could also detect APS sulfo transferase activity in some higher plants by this method.