A fluorescence study of thermally induced conformational changes in yeast hexokinase

Fluorescence studies have been performed on yeast hexokinase (ATP: D-hexose 6-phosphotransferase, EC 2.7.1.1) as a function of temperature. Observations of both the intrinsic protein fluorescence and the fluorescence of the noncovalently bound apolar probe 2-(p-toluidinyl)naphthalene-6-sulfonic acid under conditions where hexokinase is monomeric, indicate that significant thermal structural transitions occur in the protein over the physiological range of temperature (0 degrees-40 degrees C) and that there are different temperature-dependent forms of the enzyme. Thermal transitions between these forms are affected by the binding of the substrates D-glucose and ATP-Mg. It therefore appears that catalysis connects conformers that differ in stability and the present results are consistent with models in which hexokinase function is linked to changes in the interactions between the domains into which this protein is folded.