Characterization of an adenosine 5'-triphosphate- and deoxyadenosine 5'-triphosphate-activated nucleotidase from...

The kinetic properties of a soluble, magnesium-dependent 5'-nucleotidase from human malignant lymphocytes have been determined. The partially purified enzyme is distinct from plasma membrane-associated 5'-nucleotidase and is free of nonspecific phosphatase activity. Among purine ribonucleotides, it reacted efficiently with inosine 5'-monophosphate and guanosine 5 -monophosphate and to a lesser degree with deoxyguanosine 5'-monophosphate. Adenosine 5'-monophosphate and deoxyadenosine 5'-monophosphate were 30-fold less efficient substrates. Increasing concentrations of adenosine 5'-triphosphate and deoxyadenosine 5'-triphosphate from 0 to 3 mM enhanced 5'-nucleotidase activity up to 7-fold. Guanosine 5'-triphosphate and deoxyguanosine 5'-triphosphate were much less effective enzyme activators, while uridine 5'-triphosphate was without effect. Inorganic phosphate inhibited dephosphorylating activity in both adenosine 5'-triphosphate-supplemented and unsupplemented buffer. The activation of this 5'-nucleotidase by deoxyadenosine 5'-triphosphate, combined with the relative inability of the enzyme to dephosphorylate deoxyadenosine 5'-monophosphate, conceivably may contribute to the adenine nucleotide degradation induced by deoxyadenosine in normal and malignant lymphocytes.