CONFORMATIONAL EQUILIBRIUM OF DIHYDRONICOTINAMIDE IN LDH-NADH

The dihydronicotinamide ring pucker of NADH bound to LDH is examined b y exchange-transferred nuclear Overhauser nmr and by free energy molec ular dynamics simulations. The influence of the enzyme-cofactor intera ctions on the conformational equilibrium of ring pucker was investigat ed in order to assess the potential role of steric strain in catalysis and stereospecificity of hydride transfer. Results presented here sho w that binding produces no constraint on the ring flexibility, therefo re steric strain of the ring is not important. However, a second confo rmational feature - the configuration of the ring nitrogen - is pertur bed by the enzyme and this effect may have consequences in catalysis.