Purification and properties of the ATP sulphurylase of rat liver.

ATP sulphurylase (ATP:sulphate adenylyltransferase, EC 2.7.7.4) as been purified about 2500-fold from rat liver. It was free of ATPase, inorganic pyrophosphatase, adenosine phosphosulphate kinase and ADP sulphurylase activities. The enzyme was homogeneous to chromatography on Sepharose 4B and to density-gradient sedimentation; it was not homogeneous to acrylamide gel electrophoresis nor to sedimentation in the ultracentrifuge. Possible reasons for this heterogeneity are considered. The molecular weight of the enzyme is 410 000 as measured by chromatography on Sepharose 4B. The v is 0.80, suggesting that ATP sulphurylase is a lipoprotein. The enzyme activity is associated with a pigment having a lambdamax of 410 nm. Studies of the forward, reverse and ATP-PPi exchange reactions catalysed by ATP sulphurylase have shown that these are sequential bi-bi reactions, with ATP being the first substrate bound and adenosine phosphosulphate the last product released. The results are incompatible with previous suggestions that the ATP sulphurylase of rat liver catalysed a bi-bi ping-pong reaction.