Purification and properties of 3′-nucleotidase of Leishmania donovani

A surface membrane 3′-nucleotidase from Leishmania donovani promastigotes has been purified to SDS/PAGE homogeneity. The enzyme has apparent subunit molecular mass of 38 kDa, pI 5.8 and a broad pH optimum, 5.5-7.5. EDTA partially inhibited the enzyme activity, which was fully restored by Co2+; Mg2+, Ca2+ or Mn2+ had no effect on the activity. ZnCl2 or dithiothreitol at 1 mM was inhibitory at pH 7.5, but was without effect at pH 5.5, whereas at both pH values 5 mM of either compound inhibited the enzyme. The substrate-specificity of the purified enzyme is restricted to ribonucleoside 3′-phosphates. 3′-AMP and 3′-IMP are the best substrates, whereas ADP, ATP, 2′-deoxyadenosine 3′-phosphate and 5′-AMP are competitive inhibitors of the enzyme. The enzyme showed low latency in intact-cell preparations. The kinetic properties and the surface membrane localization of the enzyme suggest its implication in the formation of nucleosides from 3′-nucleotides of the parasite's host.