Specificities of reactivating factors for adenosylcobalamin-dependent diol dehydratase and glycerol dehydratase

Adenosylcobalamin-dependent glycerol and diol dehydratases undergo inactivation by the physiological substrate glycerol during catalysis. In the permeabilized cells of Klebsiella pneumoniae, Klebsiella oxytoca, and recombinant Escherichia coli, glycerol-inactivated glycerol dehydratase and diol dehydratase are reactivated by their respective reactivating factors in the presence of ATP, Mg2+, and adenosylcobalamin. Both of the reactivating factors consist of two subunits. To examine the specificities of the reactivating factors, their genes or their hybrid genes were co-expressed with dehydratase genes in E. coli cells in various combinations. The reactivating factor of K. oxytoca for diol dehydratase efficiently cross-reactivated the inactivated glycerol dehydratase, whereas the reactivating factor of K. pneumoniae for glycerol dehydratase hardly cross-reactivated the inactivated diol dehydratase. Both of the two hybrid reactivating factors rapidly reactivated the inactivated glycerol dehydratase. In contrast, the hybrid reactivating factor containing the large subunit of the glycerol dehydratase reactivating factor hardly reactivated the inactivated diol dehydratase. These results indicate that the glycerol dehydratase reactivating factor is much more specific for the dehydratase partner than the diol dehydratase reactivating factor and that a large subunit of the reactivating factors principally determines the specificity for a dehydratase.