The Enzymatically Catalyzed Mutarotation.

1. The free energy, enthalpy, and entropy of activation of the enzymatically catalyzed mutarotation of glucose have been determined: ΔG* 11.9 kcal/mol, ΔH* 12.8 kcal/mol, ΔS* 3.1 cal × mol^-1 × K^-1. 2. The pH-dependence of the enzymatic activity has been investigated. The active center of the mutarotase from Escherichia coli contains one functional group (pK 5.5) which in the dissociated form has only a catalytic function, and a second one (pK 7.6) which is responsible for the binding of the substrate. 3. The binding group of the substrate has been determined. By comparing the Michaelis and inhibitor constants of a variety of substrates and inhibitors it is concluded that the substrate is bound to the enzyme over an equatorial hydroxyl group at C-2 of the carbohydrate ring. 4. The products of the enzymatically catalyzed mutarotation have been analyzed by gas chromatography. These experiments show that the mutarotase catalyzes not only the anomerisation but also the ring isomerisation. The result is interpreted as evidence of an acyclic intermediate of the mutarotation of the aldoses. 5. The results are summarized in a reaction mechanism of the enzymatically catalyzed mutarotation. Its characteristic feature is that it describes the action of the mutarotase from E. coli as a base catalysis. [ABSTRACT FROM AUTHOR]