title: Small-Molecule Allosteric Activation of Human Glucokinase in the Absence of Glucose.
abstract: Synthetic allosteric activators of human glucokinase are receiving considerable attention as potential diabetes therapeutic agents. Although their mechanism of action is not fully understood, structural studies suggest that activator association requires prior formation of a binary enzyme-glucose complex. Here, we demonstrate that three previously described activators associate with glucokinase in a glucose-independent fashion. Transient-state kinetic assays reveal a lag in enzyme progress curves that is systematically reduced when the enzyme is preincubated with activators. Isothermal titration calorimetry demonstrates that activator binding is enthalpically driven for all three compounds, whereas the entropic changes accompanying activator binding can be favorable or unfavorable. Viscosity variation experiments indicate that thekcatvalue of glucokinase is almost fully limited by product release, both in the presence and absence of activators, suggesting that activators impact a step preceding product release. The observation of glucose-independent allosteric activation of glucokinase has important implications for the refinement of future diabetes therapeutics and for the mechanism of kinetic cooperativity of mammalian glucokinase.
authors.affiliation: Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, United States.
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Bowler
authors.forename: Katherine L
authors.initials: KL
authors.lastname: Hervert
authors.forename: Mark L
authors.initials: ML
authors.lastname: Kearley
authors.forename: Brian G
authors.initials: BG
authors.lastname: Miller
keywords: Maturity onset diabetes of the young type II; glucokinase activators; hysteretic enzyme; kinetic cooperativity