A soluble nitric oxide synthase (NOS) activity was purified 2800-fold from Leishmania donovani, the causative parasite of visceral leishmaniasis, by two-step affinity and anion-exchange chromatography. The purified enzyme ran as a prominent band of 110 kDa on SDS-PAGE whereas gel filtration experiments estimated the native molecular mass to be 230±20 kDa indicating that the native enzyme exists as a dimer. The enzyme activity required NADPH and was blocked by EGTA. The enzyme kinetics, cofactor requirements, inhibition studies and Western blot analysis with brain anti-NOS antibody suggest its similarity with mammalian NOS isoform I
