ATP-DIPHOSPHOPHYDROLASE ACTIVIN IN RAT-HEART TISSUE

Extracellular nucleotides interact with specific receptors on the cell surface and are locally metabolized by ecto-nucleotidases. Biochemica l characterization of the ATPase and ADPase activities detected in rat heart sarcolemma, under conditions where mitochondrial ATPase and ade nylate kinase were blocked, suppor:s our proposal that both activities correspond to a single enzyme, known as ATP-diphosphohydrolase or apy rase. The physiological function of this enzyme could be dephosphoryla tion of the nucleotides present in the interstitial heart compartment acting together with 5'-nucleotidase. Both hydrolytic activities have similarities in: sarcolemma localization, bivalent metal ion dependenc e, optimum pH, effect of several amino acid residue modifiers, competi tive inhibition of nucleotide analogs, and broad nucleoside di- and tr iphosphate specificity. The ATPase activity could not be separated fro m the ADPase either through isoelectrofocusing or electrophoresis unde r acid conditions.