Conformational variability of NAD+ in the free and bound states: a nicotinamide sandwich in NAD+ crystals

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Science  23 Nov 1984:
Vol. 226, Issue 4677, pp. 969-971
DOI: 10.1126/science.6239374


X-ray analysis of the free-acid crystal form of the coenzyme nicotinamide adenine dinucleotide (NAD+) revealed a conformational difference between the free NAD+ molecule and one bound in enzymes or complexed to Li+ ions. The pyrophosphate group showed asymmetry in the phosphate-oxygen bonds of the phosphate-oxygen-phosphate link; this bond at the nicotinamide side of the link is longer than that at the adenosine side by 0.04 angstrom. The crystal structure showed a novel intermolecular stacking of adenine and water molecules on opposite sides of nicotinamide that gives rise to a nicotinamide sandwich.