ADP sulphurylase from baker9s yeast was purified and its properties were studied. The enzyme is very heat-labile and its activity shows linear kinetics over narrow ranges of time and protein concentration. It is not activated by metals and is inhibited by thiol-reactive compounds. The enzyme, which replaces inorganic sulphate in adenosine 5′-sulphatophosphate with Pi to yield ADP, also catalyses an exchange of Pi into ADP. Kinetic studies show that the enzyme has a high affinity for adenosine 5′-sulphatophosphate, although concentrations in excess of 1.0mm are inhibitory. However, the kinetics for Pi are more complex and the enzyme is not inhibited by Pi up to 20.0mm.
