The ApbC protein has been shown previously to bind and rapidly transfer iron-sulfur ([Fe-S]) clusters to an apoprotein (Boyd, J. M., Pierik, A. J., Netz, D. J., Lill, R., and Downs, D. M. (2008) Biochemistry 47, 8195-8202. This study utilized both in vivo and in vitro assays to examine the function of variant ApbC proteins. The in vivo assays assessed the ability of ApbC proteins to function in pathways with low and high demand for [Fe-S] cluster proteins. Variant ApbC proteins were purified and assayed for the ability to hydrolyze ATP, bind [Fe-S] cluster, and transfer [Fe-S] cluster. This study details the first kinetic analysis of ATP hydrolysis for a member of the ParA subfamily of "deviant" Walker A proteins. Moreover, this study details the first functional analysis of mutant variants of the ever expanding family of ApbC/Nbp35 [Fe-S] cluster biosynthetic proteins. The results herein show that ApbC protein needs ATPase activity and the ability to bind and rapidly transfer [Fe-S] clusters for in vivo function.