A Time-dependent Transferred Nuclear Ovcrhauser Effect Study

The conformation of NAD + in tile sheep liver sorbitoi dehydrogenase-NAD + bi~lary complex has been investigated using time-dependent proton-proton transferred nuclear Overhauser enhancement measurements to determine interproton distance ratios and distances between bound NAD + protons. The conformation about both the adenosine and .nieotinamide riboside glycosidic bonds is anti, the conformations of the adenosine and nicotinamide ribose rings are C3'-endo and C l'-exo, respectively, and the conformations about the addnosine and nicotinamide riboside C4'-C5' bonds are g+ and t, respectively, similar to those found in complexes of NAD+:with other A type dehydrogenases. In addition, however, the distance data are indicative of an unusual overall conformation of NAD + in the sorbitol dehydrogenase-NAD + binary complex, with the planes of the nicotinamide and adenine rings separated by 6 to 8 A and at approximately 120 ° to each other. This overall conformation differs from the concensus extended conformation found in the NAD+-dehydrogenase complexes crystallized to date, where the planes of the nicotinamide and adenine rings are 12 to 14 A apart and nearly perpendicular to each other.