Photodependent inhibition of bovine spleen NAD+ glycohydrolase by 8-azido carbocyclic analogs of NAD+.

Carba-NAD+ and pseudocarba-NAD+, and their 8-azidoadenosyl derivatives, were found to be good competitive inhibitors of calf spleen NAD+ glycohydrolase. The 8-azido compounds, tested as photoaffinity labels, inhibited the enzyme in a light- and time-dependent manner; this inhibition could be prevented by 3-aminopyridine adenine dinucleotide (n3PdAD+), a competitive inhibitor of NAD+ glycohydrolase. Irradiation in the presence of the [3H]-labeled 8-azido-carba-NAD+ derivative resulted in an irreversible incorporation of the radioactivity into the enzyme that could be largely prevented by addition of n3PdAD+. These results indicate that carbocyclic-analogs of NAD+ will be useful in identifying the substrate binding site of NAD+ glycohydrolase.