title: Further evidence for the reliance of catalysis by rabbit muscle pyruvate kinase upon isomerization of the ternary complex between enzyme and products.
abstract: Isothermal calorimetry has been used to examine the effect of thermodynamic non-ideality on the kinetics of catalysis by rabbit muscle pyruvate kinase as the result of molecular crowding by inert cosolutes. The investigation, designed to detect substrate-mediated isomerization of pyruvate kinase, has revealed a 15% enhancement of maximal velocity by supplementation of reaction mixtures with 0.1 M proline, glycine or sorbitol. This effect of thermodynamic non-ideality implicates the existence of a substrate-induced conformational change that is governed by a minor volume decrease and a very small isomerization constant; and hence, substantiates earlier inferences that the rate-determining step in pyruvate kinase kinetics is isomerization of the ternary enzyme product complex rather than the release of products.
authors.affiliation: Department of Biochemistry, School of Molecular and Microbial Sciences, University of Queensland, Brisbane, Qld 4072, Australia.
authors.forename: Thierry G A
authors.initials: TG
authors.lastname: Lonhienne
authors.forename: Paul E B
authors.initials: PE
authors.lastname: Reilly
authors.forename: Donald J
authors.initials: DJ
authors.lastname: Winzor
mesh_terms: D000818:Animals; D002384:Catalysis; D003124:Colorimetry; D004789:Enzyme Activation; D005998:Glycine / Q000737:chemistry; D007536:Isomerism; D007700:Kinetics; D009132:Muscles / Q000201:enzymology*; D011392:Proline / Q000737:chemistry; D011770:Pyruvate Kinase / Q000737:chemistry* / Q000378:metabolism; D011817:Rabbits; D013012:Sorbitol / Q000737:chemistry; D013379:Substrate Specificity; D013816:Thermodynamics; D014461:Ultracentrifugation
chemical_list: D013012:Sorbitol; D011392:Proline; D011770:Pyruvate Kinase; D005998:Glycine