Glycerol 3-Phosphate Dehydrogenase: Role of the Protein Conformational Change in Activation of a Readily Reversible Enzyme-Catalyzed Hydride Transfer Reaction

Abstract

4B) GPDH-catalyzed hydride transfer from ethylene glycol (EtG) to NAD. These are combined with the previously determined kinetic parameters for hydride transfer from NADH to GA 29 to give reaction equilibrium constants. Our results show that there is a larger thermodynamic driving force for hydride transfer from the secondary alcohol glycerol 3phosphate (G3P) to NAD compared to hydride transfer from the primary alcohol EtG. This difference in substrate reactivity Scheme 1. (A) The Hydride Transfer Reaction Catalyzed by GPDH; (B) Transition State Stabilization by (i) Interactions with the Substrate Phosphodianion Determined from the Ratio of Second-Order Rate Constants for Reactions of Whole and Truncated Substrates; (ii) Interactions with Phosphite Dianion Determined From the Ratio of Second-and Third-Order Rate Constants, Respectively, for Unactivated and Dianion-Activated Reactions of the Truncated Substrate Scheme 2. Induced-Fit Mechanism for Phosphite Dianion Activation of GPDH-Catalyzed Hydride Transfer to GA to Form EtG 20,25 Scheme 3. Dianion Activation of GPDH-Catalyzed Reduction of GA by Direct Stabilization of the Transition State for Hydride Transfer 26 Scheme 4. Reversible Unactivated and Phosphite-Dianion-Activated GPDH-Catalyzed Hydride Transfer from EtG to NAD Biochemistry pubs.acs.org/biochemistry Article