Purification, Crystallization, and Subunit Structure of Allosteric Adenosine 5′-Monophosphate Nucleosidase

Adenosine monophosphate nucleosidase (adenosine monophosphate phosphoribohydrolase, EC 3.2.2.4) has been purified from Azotobacter vinelandii strain OP. The purified enzyme preparation was homogeneous as judged by analytical ultracentrifugation and polyacrylamide gel electrophoresis. Following purification, the enzyme was crystallized from ammonium sulfate solutions. The molecular weight of the enzyme was approximately 370,000 as determined from gel filtration and sedimentation velocity experiments, while a molecular weight of approximately 325,000 was obtained from the Archibald approach to equilibrium method. Results of polyacrylamide gel electrophoresis in sodium dodecyl sulfate or 9 m urea, as well as analysis of amino acid composition, suggest that the enzyme consists of similar polypeptide chains having a molecular weight of approximately 57,000. The crystalline enzyme differs from previously described preparations of AMP nucleosidase in that the substrate- or salt-induced association-dissociation reaction does not occur.