Characterization of a filtrable 3'-nucleotidase of Leishmania donovani.

A plasma membrane 3'-nucleotidase (3'-ribonucleotide phosphohydrolase, EC 3.1.3.6) having a apparent subunit molecular mass of 38 kDa but filtrable through a Centriprep-10 microconcentrator (Amicon) membrane was purified from Leishmania donovani promastigotes. The enzyme activity has an optimum at pH around 7.5. EDTA strongly inhibited the enzyme activity which was fully restored only by Co2+, from various metal ions added. Citrate ions, Zn2+ or dithiothreitol were also strongly inhibitory. The enzyme is apparently located on the inner side of the parasite plasma membrane. The substrate specificity and kinetics of the filtrable enzyme are similar to those of the non-filtrable outer-surface-membrane-bound 3'-nucleotidase reported by Gbenle and Dwyer (Gbenle, G.O. and Dwyer, D.M. (1992) Biochem. J. 285, 41-46). Therefore, it is suggested that both enzymes are implicated in the supply of nucleosides to the parasite.