Partial purification and properties of an AMP-specific soluble 5′-nucleotidase from pigeon heart

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Abstract
A soluble 5′-nucleotidase was purified 200-fold from pigeon heart. The enzyme (1) had an apparent molecular mass close to 150 kDa, (2) had a neutral pH optimum and hydrolysed a wide range of nucleoside 5′-monophosphates with a 15-fold preference for AMP over IMP, (3) at near-physiological concentrations of AMP was activated by ADP but not by ATP, (4) was inhibited by high Mg2+ concentration and high ionic strength, (5) was weakly inhibited by p-nitrophenol phosphate and Pi, and (6) was non-competitively inhibited more potently by 5′-deoxy-5′-isobutylthioinosine than by 5′-deoxy-5′-isobutylthioadenosine, but not by [alpha, beta-methylene]ADP. The data show that the enzyme is distinct from the ecto-5′-nucleotidase and from the previously purified IMP-specific 5′-nucleotidase. They also predict that the enzyme is activated during ATP catabolism and hence will generate a more-than-linear increase in the adenosine-formation rate in response to an increase in cytosolic AMP concentration.