In yeast cells, the interaction of yeast pyruvate kinase (YPK) with PEP and its allosteric effector Fructose 1,6-bisphosphate (FBP,) was found to be enhanced by the presence of Mg2+. Therefore, Mg2+ was isolated as an important component in the successful catalysis of PEP into pyruvate by pyruvate kinase. Furthermore, the metal ion Mn2+ was shown to have a similar, but stronger effect on the coupling free energy of YPK than Mg2+.