Yeast Hexokinase: Interaction with Substrates and Analogs Studied by Difference Spectrophotometry

Abstract

The mechanism of the reaction catalyzed by yeast hexokinase has been investigated by means of spectrophotometric investigations. Two binding sites, one for the sugar and one for the nucleotide substrate, have been characterized. The interaction of sugar substrates with yeast hexokinase induces spectral perturbations of aromatic residues of the protein molecule. The specificity of the enzyme towards its sugar substrates is discussed. The interaction of ATP-Mg can only be visualized spectrophotometrically when the sugar substrate or inhibitor is already bound to the enzyme. Furthermore, spectrophotometric studies evidence the formation of a binary complex (sugar · enzyme) and ternary complexes (sugar · enzyme · nucleotide) in accord with an ordered mechanism.