THE ALLOSTERIC LIGAND SITE IN THE V-MAX-TYPE COOPERATIVE ENZYME PHOSPHOGLYCERATE DEHYDROGENASE

The crystal structure of the phosphoglycerate dehydrogenase from Esche richia coli is unique among dehydrogenases. It consists of three clear ly separate domains connected by flexible hinges. The tetramer has app roximate 222 symmetry with the principal contacts between the subunits forming between either the nucleotide binding domains or the regulato ry domains. Two slightly different subunit conformations are present w hich vary only in the orientations of the domains. There is a hinge-li ke arrangement near the active site cleft and the serine effector site is provided by the regulatory domain of each of two subunits. Interdo main flexibility may play a key role in both catalysis and allosteric inhibition.