Large subunit of the diol dehydratase-reactivating factor (DDR), which reactivates suicidally inhibited adenosylcobalamin-dependent diol dehydratase (DD, pddA, pddB, pddC). DDR acts as a chaperone, reactivating inactivated DD holoenzyme in the presence of ATP, Mg(2+) and free adenosylcobalamin (AdoCbl), by mediating the exchange of the tightly bound damaged cofactor AdoCbl for a free intact one (PubMed:10529189, PubMed:9405397, PubMed:9920879, PubMed:17916188, PubMed:18586770, PubMed:21040475). Reactivation takes place in two steps: ADP-dependent cobalamin release, then ATP-dependent dissociation of the DD apoenzyme-DDR complex. DDR has weak ATPase activity which is required for DD reactivation (PubMed:10529189, PubMed:17916188, PubMed:21040475). This subunit contains the adenosine nucleotide binding site (PubMed:16338403). Activates glycerol-inactivated, O2-inactivated holoenzyme and inactivated enzyme-cyanocobalamin complex (PubMed:9920879). Also reactivates glycerol-inactivated hologlycerol dehydratase, a DD isozyme (PubMed:17916188). ATP + H2O = ADP + H(+) + phosphate One Mg(2+)is bound by the enzyme, a second binds only to the beta-phosphate of DdrA-bound ADP (PubMed:16338403). Co(2+), Mn(2+) and Ni(2+) can substitute in vitro (PubMed:21040475). kcat for enzyme-bound damaged AdoCbl is 0.14 min(-1), kcat for reactivation of CN-Cbl-inactivated enzyme is 0.27 min(-1). Component of the DDR complex, a heterotetramer of DdrA(2)/DdrB(2) (Probable) (PubMed:9920879, PubMed:10529189, PubMed:16338403, PubMed:17916188, PubMed:21040475). The DDR complex interacts with the diol dehydratase complex in the presence of ADP but not ATP (PubMed:10529189, PubMed:21040475). Belongs to the DdrA/PduG family.