CNAD - A POTENT AND SPECIFIC INHIBITOR OF ALCOHOL-DEHYDROGENASE

CNAD(5-beta-D-ribofuranosylnicotinamide adenine dinucleotide) is an isosteric and isomeric analogue of NAD, in which the nicotinamide ring is linked to the sugar via a C-glycosyl (C5-C1') bond. CNAD acts as a general dehydrogenase inhibitor but shows unusual specificity and affinity for liver alcohol dehydrogenase (ADH, EC 1.1.1.1). The pattern of inhibition is competitive, with Ki similar or equal to 4 nM, with NAD as the variable substrate. These values are 3-5 orders of magnitude smaller than those obtained for CNAD in other dehydrogenases and are comparable to values observed for the tightest binding ADH inhibitors known. The specificity and affinity of CNAD for ADH are likely due to coordination of the zinc cation at the ADH catalytic site by the CNAD pyridine nitrogen. This is supported by kinetic and computational studies of ADH-CNAD complexes. These results are compared with those for a related analogue, CPAD. In this analogue, displacement of the pyridine nitrogen to the opposite side of the ring removes the specificity for ADH.