Lactate dehydrogenase catalyzes the oxidation of lactate by facilitating the direct, simultaneous transfer of a proton and two electrons to the coenzyme, NAD+. Because many other dehydrogenases operate in a similar manner, the proposed research serves as a model for future explanations of how dehydrogenases accomplish large accelerations of chemical reactions. Using both chemical kinetics and Raman spectroscopy to determine changes in the chemical bonds of both the substrate and coenzyme upon binding to the enzyme, these changes to the structure, which is known, of the enzyme with substrate and coenzyme bound will be related. These studies will partially involve the synthesis of isotopically labeled substrates and coenzymes so that Raman bands can be assigned to the molecular motions of these molecules both in solution and bound to enzyme. These studies also will be extended to formate dehydrogenase to produce a more general picture of the interactions that occur. Recent work shows that to a large extent enzymes use noncovalent interactions to facilitate the making and breaking of covalent bonds and to make or break them sterically. Because the energies of noncovalent interactions are not easily assessed during an enzyme reaction a description of the contributions to enzyme catalysis provided by various types of noncovalent interactions is a difficult yet important goal, and the possibility of rationalizing enzymic reactions in terms of the observed rate effects produced by simple catalysts has been the goal of enzyme chemists for many years. Because of this work this may be possible for NAD dependent dehydrogenasis.
