Abstract
cN-II class of 5' purine nucleotidases exhibit specificity for IMP/GMP and belong to the HAD (haloacid dehalogenase) superfamily of hydrolases. The recently identified ISN1 class of IMP specific 5'-nucleotidases occurring in yeast, fungi and certain Plasmodia lack sequence homology with the cN-II class of enzymes. We show from analysis of motif and fold conservation that ISN1s also belong to the HAD superfamily. This identification adds a new novel member to this superfamily.