Abstract
Adenosine 5'-(S)-[16O,17O,18O]phosphate was pyrophosphorylated by the combined action of adenylate kinase and pyruvate kinase. The isotopomers of adenosine 5'-[alpha-16O,17O,18O]triphosphate were hydrolysed by venom 5'-nucleotide phosphodiesterase (Crotalus adamanteus) in H2(17)O. Analysis by 31P nuclear magnetic resonance spectroscopy of the resulting adenosine 5'-[16O,17O,18O]phosphate, after cyclization and esterification, showed that the hydrolysis occurs with retention of configuration at phosphorus. The most likely explanation of this observation is that the enzymic hydrolysis involves a double displacement at phosphorus with a covalent nucleotidyl--enzyme intermediate on the reaction pathway.