A dimeric Dictyostelium nucleoside diphosphate kinase has been stabilized by the double mutation P100S-N150stop which targets residues involved in the trimer interface (Karlsson, A., Mesnildrey, S., Xu, Y., Moréra, S., Janin, J., and Veron, M. (1996) J. Biol. Chem. 271, 19928-19934). The reassociation of this dimeric form into a hexamer similar to the wild-type enzyme is induced by the presence of a nucleotide substrate. Equilibrium sedimentation and gel filtration experiments, as well as enzymatic activity measurements, show that reactivation of the enzyme closely parallels its reassociation. A phosphorylatable intermediate with low activity participates in the association pathway while the dimeric form is shown totally devoid of enzymatic activity. Our results support the hypothesis that different oligomeric species of nucleoside diphosphate kinase are involved in different cellular processes where the enzymatic activity is not required.