NAD+ catabolism in pheochromocytoma rat cells

The catabolic pathway of nicotinamide adenin dinucleotide (NAD) in cultured pheochromocytoma rat cells (PC12) was investigated. The first evidence obtained in these studies was that, despite inducing cell differentiation, NGF treatment did not modify NAD catabolism. Following incubation of PC12 homogenate with NAD, ADP-ribose, AMP, IMP, and HYP was produced. The catabolic fate of AMP and ADPR so obtained was followed by monitoring to a final production of inosine and hypoxanthine through several enzymatic steps. When intact PC12 cells were incubated with NAD in the culture medium AMP, IMP and HYP were found but, no ADPR and cADPR were present in the growth medium. "Nucleotides analyses" carried out on the homogenate obtained from these cells, confirmed the absence of cADPR and an increase of intracellular ADPR. These results led us to believe that in PC12 cells the ADP ribosyl cyclase activity is absent and that NADase is an ecto-enzyme able to transfer the ADPR, produced from NAD catabolism, inside the cells.