title: Structure-Reactivity Effects on Intrinsic Primary Kinetic Isotope Effects for Hydride Transfer Catalyzed by Glycerol-3-phosphate Dehydrogenase.
abstract: Primary deuterium kinetic isotope effects (1°DKIE) on (kcat/KGA, M-1s-1) for dianion (X2-) activated hydride transfer from NADL to glycolaldehyde (GA) catalyzed by glycerol-3-phosphate dehydrogenase were determined over a 2100-fold range of enzyme reactivity: (X2-, 1°DKIE); FPO32-, 2.8 ± 0.1; HPO32-, 2.5 ± 0.1; SO42-, 2.8 ± 0.2; HOPO32-, 2.5 ± 0.1; S2O32-, 2.9 ± 0.1; unactivated; 2.4 ± 0.2. Similar 1°DKIEs were determined for kcat. The observed 1°DKIEs are essentially independent of changes in enzyme reactivity with changing dianion activator. The results are consistent with (i) fast and reversible ligand binding; (ii) the conclusion that the observed 1°DKIEs are equal to the intrinsic 1°DKIE on hydride transfer from NADL to GA; (iii) similar intrinsic 1°DKIEs on GPDH-catalyzed reduction of the substrate pieces and the whole physiological substrate dihydroxyacetone phosphate. The ground-state binding interactions for different X2-are similar, but there are large differences in the transition state interactions for different X2-. The changes in transition state binding interactions are expressed as changes in kcatand are proposed to represent changes in stabilization of the active closed form of GPDH. The 1°DKIEs are much smaller than observed for enzyme-catalyzed hydrogen transfer that occurs mainly by quantum-mechanical tunneling.
authors: Department of Chemistry, University at Buffalo, SUNY , Buffalo, New York 14260-3000, United States.
authors: Archie C
authors: AC
authors: Reyes
authors: Department of Chemistry, University at Buffalo, SUNY , Buffalo, New York 14260-3000, United States.
authors: Tina L
authors: TL
authors: Amyes
authors: Department of Chemistry, University at Buffalo, SUNY , Buffalo, New York 14260-3000, United States.
authors: John P
authors: JP
authors: Richard
mesh_terms: D002384:Catalysis; D005993:Glycerolphosphate Dehydrogenase / Q000737:chemistry*; D007554:Isotopes / Q000737:chemistry*; D007700:Kinetics; D013329:Structure-Activity Relationship; D013816:Thermodynamics
chemical_list: D007554:Isotopes; D005993:Glycerolphosphate Dehydrogenase