Phosphoglycerate kinase (EC ) catalyzes reversible phosphoryl trans-fer from 1,3-bisphosphoglycerate to ADP to synthesize 3-phosphoglycerate and ATP during glycolysis. Phosphoglycerate kinases from several sources can use GDP⁄GTP as alternative substrates to ADP⁄ATP; however, the maximal velocities (Vm) reached with the guanine nucleotides are 50% of those displayed with the adenine nucleotides.