 This zinc ion forms tetrahedral dipole interactions between the amino acid residues Asp173, His256, and His274 as well as a water molecule.The NAD+ binding site, resembling the Rossmann fold within the N-terminal domain, extends from the surface of the enzyme to the cleft containing the active site.The nicotinamide ring (the active region of NAD+) binds in a pocket of the cleft consisting of the residues Asp100, Asp123, Ala124, Ser127, Leu129, Val131, Asp173, His174, and Phe247.