Hydrogen bonding and reaction specificity in lactate dehydrogenase studied by Raman spectroscopy

The Raman spectrum of a small molecule or molecular moiety when bound to sizable proteins can be measured by using difference techniques developed in our laboratory. We have applied this method in obtaining the Raman spectrum of the cofactor acetylpyridine adenine dinucleotide, APAD⁺, when bound to lactate dehydrogenase. The Raman data permit a characterization of some of the molecular interactions responsible for the stereochemistry of the reaction catalyzed by this enzyme. We find that the enzyme forms a strong hydrogen bond with the cofactor's carboxamide group and suggest that this is at least partially responsible for the very high degree of stereochemistry fidelity observed with this enzyme.