Inhibition of extracellular and purified 5'-nucleotidase from rat heart

5'-Nucleotidase in perfused rat hearts, accessible to extracellular substrate [14C]-AMP contained in the perfusate, was compared to a partially purified 5'-nucleotidase from the same organ. Both activities were inhibited by ATP and, more effectively, by the ADP analog adenosine-alpha, beta-methylene diphosphate (APCP). The isolated enzyme showed a competitive inhibitor constant of 5.4 x 10(-8) M for APCP (Km of AMP = 1.4 x 10(-5) M). Although both activities were effectively inhibited by APCP, insufficient knowledge about the selectivity of this agent as a nucleotidase inhibitor does not permit a conclusion on whether or not the extracellular activity is identical to the partially purified enzyme.