ENZYMATIC-ACTIVITIES AFFECTING EXOGENOUS NICOTINAMIDE ADENINE-DINUCLEOTIDE IN HUMAN SKIN FIBROBLASTS

The fate of nicotinamide adenine dinucleotide (NAD), AMP, and ADP-ribo se supplied to intact human skin fibroblasts was monitored, and the co ncentrations of intra- and extracellular pyridine and purine compounds were determined by HPLC analysis. Two enzymatic activities affecting extracellular NAD were detected on the plasma membrane, one hydrolyzin g the pyrophosphoric bond and yielding nicotinamide mononucleotide (nu cleotide pyrophosphatase) and the other cleaving the glycoside link an d releasing nicotinamide (NAD-glycohydrolase). No AMP or ADP-ribose wa s found in the extracellular medium of cells incubated with NAD, the f ormer being completely catabolized to hypoxanthine and the latter degr aded to adenine and hypoxanthine. (C) 1996 Wiley-Liss, Inc.