Abstract
Production of adenosine 5''-[35S]sulfatophosphate by a partially purified ATP sulfurylase from A. cylindrica was inhibited by AMP, ADP and Pi. Decreases in enzyme activity in the presence of these inhibitors were reversed by increasing the concentrations of ATP. The adenine nucleotides inhibited the enzyme competitively with respect to ATP. In the presence of Pi, ATP showed a positive co-operative effect on enzyme activity. The inhibition by Pi was enhanced by increasing concentrations of Mg2+. The effects of the adenine nucleotides and the interaction of Pi and Mg2+ on ATP sulfurylase activity are discussed in relation to the regulation of sulfate assimilation via the energy metabolism of the alga.