Phosphoenolypyruvate synthetase of Escherichia coli: molecular weight, subunit composition, and identification of phosphohistidine in phosphoenzyme intermediate.

Phosphoenolypyruvate synthetase of Escherichia coli has been shown to be a dimer of molecular weight 150,000. The constituent subunits appear to be identical. The enzyme tends to dissociate to monomers at low protein concentration, but the tendency is much diminished in the phosphoenzyme form, suggesting that enzyme phosphorylation is accompanied by a structural rearrangement in the subunit contact domain. The enzyme appears to show half of the sites reactivity with respect to its phosphorylation by ATP. Several lines of evidence, including identification of 3-phosphohistidine in alkaline digests of the phosphoenzyme, indicate that a histidyl residue is the site of phosphorylation.