Influence of phosphoenolpyruvate and magnesium ions on the quaternary structure of enzyme I of the phosphotransferase system from gram-positive bacteria.

Solution X-ray scattering patterns of enzyme I of the phosphotransferase system from Staphylococcus carnosus indicate an increase in radius of gyration and molecular mass in the presence of Mg2+ or both Mg2+ and phosphoenolpyruvate, indicating a partial dimerization of enzyme I. Mg2+ ions are essential for both the dimerization and the activation, whereas the substrate phosphoenolpyruvate shifts the monomer--dimer equilibrium to the enzymatically active dimer by decreasing the dissociation rate of the phosphorylated dimer.