RESUMEN
The nucleoside triphosphate hydrolases that are produced by Neospora caninum (NcNTPase) and Toxoplasma gondii (TgNTPase-I) have a different physiological function from the ubiquitous ecto-ATPases. The recombinant enzymes were crystallized at 293â K using polyethylene glycol 3350 as a precipitant and X-ray diffraction data sets were collected for NcNTPase (to 2.8â Å resolution) and TgNTPase-I (to 3.1â Å resolution) at 100â K using synchrotron radiation. The crystals of NcNTPase and TgNTPase-I belonged to the orthorhombic space group I222 (unit-cell parameters a = 93.6, b = 140.8, c = 301.1â Å) and the monoclinic space group P2(1) (unit-cell parameters a = 87.1, b = 123.5, c = 120.2â Å, ß = 96.6°), respectively, with two NcNTPase (V(M) = 3.7â Å(3)â Da(-1)) and four TgNTPase-I (V(M) = 2.7â Å(3)â Da(-1)) molecules per asymmetric unit. SAD phasing trials using a data set (λ = 0.97904â Å) collected from a crystal of selenomethionylated NcNTPase gave an initial electron-density map of sufficient quality to build a molecular model of NcNTPase.