Chorismate Mutase/Prephenate Dehydratase from Escherichia coli K12

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Abstract
The effects of phenylalanine, NaCl and pH on the conformation of chorismate mutase [EC 5.4.99.5]/prephenate dehydratase [EC 4.2.1.51] were investigated, using measurements of far and near-UV circular dichroic spectra and UV difference spectra. At pH 8.2 in 20 mM Tris-Cl buffer the enzyme contained 10-20% helix and 40-50% .beta.-structure. There was little or no change in these values on the addition of 1 mM phenylalanine (the allosteric effector) or 0.4 M NaCl or by decreasing the pH to 7.4. Both phenylalanine and NaCl caused significant changes in the conformation of the enzyme. The most prominent of these was the movement of a tryptophan residue into a more hydrophobic environment. There was also a slight perturbation of this tryptophan when the pH was decreased to 7.4. The conformational changes can explain sigmoidal kinetic behavior observed previously.