title: Modulation of glucokinase by glucose, small-molecule activator and glucokinase regulatory protein: steady-state kinetic and cell-based analysis.
abstract: GK (glucokinase) is an enzyme central to glucose metabolism that displays positive co-operativity to substrate glucose. Small-molecule GKAs (GK activators) modulate GK catalytic activity and glucose affinity and are currently being pursued as a treatment for Type 2 diabetes. GK progress curves monitoring product formation are linear up to 1 mM glucose, but biphasic at 5 mM, with the transition from the lower initial velocity to the higher steady-state velocity being described by the rate constant kact. In the presence of a liver-specific GKA (compound A), progress curves at 1 mM glucose are similar to those at 5 mM, reflecting activation of GK by compound A. We show that GKRP (GK regulatory protein) is a slow tight-binding inhibitor of GK. Analysis of progress curves indicate that this inhibition is time dependent, with apparent initial and final Ki values being 113 and 12.8 nM respectively. When GK is pre-incubated with glucose and compound A, the inhibition observed by GKRP is time dependent, but independent of GKRP concentration, reflecting the GKA-controlled transition between closed and open GK conformations. These data are supported by cell-based imaging data from primary rat hepatocytes. This work characterizes the modulation of GK by a novel GKA that may enable the design of new and improved GKAs.
authors: Pfizer Global Research and Development, Eastern Point Road, Groton, CT 06340, USA.
authors: Francis J
authors: FJ
authors: Bourbonais
authors: Jing
authors: J
authors: Chen
authors: Cong
authors: C
authors: Huang
authors: Yanwei
authors: Y
authors: Zhang
authors: Jeffrey A
authors: JA
authors: Pfefferkorn
authors: James A
authors: JA
authors: Landro
mesh_terms: D000494:Allosteric Regulation; D000818:Animals; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002478:Cells, Cultured; D054313:Drug Agonism; D004789:Enzyme Activation / Q000187:drug effects; D005941:Glucokinase / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology*; D022781:Hepatocytes / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008954:Models, Biological; D011487:Protein Conformation; D051381:Rats; D054852:Small Molecule Libraries
chemical_list: D002352:Carrier Proteins; D054852:Small Molecule Libraries; C080906:glucokinase regulatory protein; D005941:Glucokinase; D005947:Glucose