title: Experimental evidence for allosteric modifier saturation as predicted by the bi-substrate Hill equation.
abstract: The cooperative enzyme reaction rates predicted by the bi-substrate Hill equation and the bi-substrate Monod-Wyman-Changeux (MWC) equation when allosterically inhibited are compared in silico. Theoretically, the Hill equation predicts that when the maximum inhibitory effect at a certain substrate condition has been reached, an increase in allosteric inhibitor concentration will have no effect on reaction rate, that is the Hill equation shows allosteric inhibitor saturation. This saturating inhibitory effect is not present in the MWC equation. Experimental in vitro data for pyruvate kinase, a bi-substrate cooperative enzyme that is allosterically inhibited, are presented. This enzyme also shows inhibitor saturation, and therefore serves as experimental evidence that the bi-substrate Hill equation predicts more realistic allosteric inhibitor behaviour than the bi-substrate MWC equation.
authors.affiliation: Triple-J Group for Molecular Cell Physiology, Department of Biochemistry, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa.
authors.forename: A J
authors.initials: AJ
authors.lastname: Hanekom
authors.forename: J H S
authors.initials: JH
authors.lastname: Hofmeyr
authors.forename: J L
authors.initials: JL
authors.lastname: Snoep
authors.forename: J M
authors.initials: JM
authors.lastname: Rohwer
mesh_terms: D002384:Catalysis; D003198:Computer Simulation; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000737:chemistry* / Q000378:metabolism; D004798:Enzymes / Q000737:chemistry* / Q000378:metabolism; D008954:Models, Biological; D008956:Models, Chemical; D008958:Models, Molecular; D013379:Substrate Specificity
chemical_list: D004791:Enzyme Inhibitors; D004798:Enzymes