The Electronic Spectrum of the Prephenate Dianion. An Experimental and Theoretical (MD/QM) Comparison

Prephenate is the product of a Claisen rearrangement of chorismate. The enzyme chorismate mutase (CM from B. subtilis) accelerates the reaction by a factor of 106. The standard method for quantifying prephenate measures the electronic absorption spectrum after acid conversion to phenylpyruvate and subsequent alkaline treatment. To the best of our knowledge, there is no reported UV/Vis spectrum for pure prephenate. The present experimental measurement thus solves this lack of data. A novel molecular dynamics/quantum mechanics method was used to theoretically compute the electronic spectrum, and was used as supporting analysis for the new experimental spectrum. The agreement between theory and experiment is excellent in the position of the absorption peaks, their relative intensities, and their widths. A number of prephenate conformers are possible in aqueous solution, with the active conformer of CM binding just one conformer which is analogous to the dominant conformer in solution. The conformers are studied in vacuo and in the enzyme active site by ab initio quantum chemical calculations, and in solution with a classical molecular dynamics simulation. The data presented here also suggest that the electronic spectrum of prephenate bound to the chorismate mutase active site should be observed, even in the presence of other members of the aromatic amino acid pathway.