Evidence for distinct 5'- and 3'-nucleotidase activities in the surface membrane fraction of Leishmania donovani promastigotes.

A surface membrane fraction isolated from Leishmania donovani promastigotes contained distinct 5'- and 3'-nucleotidase activities. These were distinguished from each other, and from a previously described surface membrane nonspecific acid phosphomonoesterase, on the basis of several properties. The 5'- and 3'-nucleotidases had p' optima of 6.5 and 8.5, respectively. In contrast to the 3'-nucleotidase, the 5'-nucleotidase was inhibited by both ammonium molybdate and fluoride ions; the latter inducing a biphasic response. Neither divalent cations nor chelators affected the 5'-enzyme activity whereas the 3'-enzyme was inactivated by EDTA. This inactivation was fully reversed following removal of the chelator, either by resuspension of the membranes in EDTA free medium or by addition of certain divalent cations in excess; Co2+ being the most effective. The 5'-nucleotidase had activity with both ribo- and deoxyribonucleotide substrates, whereas the 3'-nucleotidase did not hydrolyse deoxyribonucleotides.