Lonhienne Thierry G A, Reilly Paul E B, Winzor Donald J
Department of Biochemistry, School of Molecular and Microbial Sciences, University of Queensland, Brisbane, Qld 4072, Australia.
Biophys Chem. 2003 May 1;104(1):189-98. doi: 10.1016/s0301-4622(02)00366-6.
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.
