A pyrophosphatase which degrades NAD+ is located on the external surface of cultured fibroblasts: evidence that NAD+ is not extruded during treatment with N-methyl-N'-nitro-N-nitrosoguanidine

The Effect of Exercise on the Skin Content of the Reduced Form of NAD and Its Response to Transient Ischemia and Reperfusion in Highly Trained Athletes

Reduced nicotinamide adenine dinucleotide (NADH) is synthesized in the cellular nucleus, cytoplasm and mitochondria but oxidized into NAD+ almost exclusively in mitochondria. Activation of human skin by the 340 nm ultraviolet light triggers natural fluorescence at the light length of 460 nm, which intensity is proportional to the skin NADH content. This phenomenon is used by the Flow Mediated Skin Fluorescence (FMSF) which measures changes in the skin NADH content during transient ischemia and reperfusion. We examined the effects of exercise to exhaustion on the skin changes of NADH in response to 200 s forearm ischemia and reperfusion in 121 highly trained athletes (94 men and 27 women, long-distance running, triathlon, taekwondo, rowing, futsal, sprint running, fencing, and tennis). We found that exercise until exhaustion changes the skin content of NADH, modifies NADH turnover at rest, during ischemia and reperfusion in the most superficial living skin cells. Compared to the pre-exercise, there were significant increases in: mean fluorescence recorded during rest as the baseline value (B mean) (p < 0.001), the maximal fluorescence that increased above the baseline during controlled forearm ischemia (FImax) (p < 0.001, only in men), the minimal fluorescence after decreasing below the baseline during reperfusion (FRmin) (p < 0.001 men; p < 0.01 women) and the difference between B mean and FRmin (R min) (p < 0.01), and reductions in the difference between FImax and B mean (I max) (p < 0.001) and I max/IRampl ratio (CImax) (p < 0.001) after the incremental exercise test. There was no statistical difference between pre- and post-exercise the maximal range of the fluorescence change during ischemia and reperfusion (IRampl). In conclusion, exercise to exhaustion modifies the skin NADH content at rest, during ischemia and reperfusion as well as the magnitude of changes in the NADH caused by ischemia and reperfusion. Our findings suggest that metabolic changes in the skin NADH accompanying exercise extend beyond muscles and affect other cells and organs.

Enzymology of NAD+ synthesis

Beyond its role as an essential coenzyme in numerous oxidoreductase reactions as well as respiration, there is growing recognition that NAD+ fulfills many other vital regulatory functions both as a substrate and as an allosteric effector. This review describes the enzymes involved in pyridine nucleotide metabolism, starting with a detailed consideration of the anaerobic and aerobic pathways leading to quinolinate, a key precursor of NAD+. Conversion of quinolinate and 5'-phosphoribosyl-1'-pyrophosphate to NAD+ and diphosphate by phosphoribosyltransferase is then explored before proceeding to a discussion the molecular and kinetic properties of NMN adenylytransferase. The salient features of NAD+ synthetase as well as NAD+ kinase are likewise presented. The remainder of the review encompasses the metabolic steps devoted to (a) the salvaging of various niacin derivatives, including the roles played by NAD+ and NADH pyrophosphatases, nicotinamide deamidase, and NMN deamidase, and (b) utilization of niacins by nicotinate phosphoribosyltransferase and nicotinamide phosphoribosyltransferase.

Enzymatic activities affecting exogenous nicotinamide adenine dinucleotide in human skin fibroblasts

The fate of nicotinamide adenine dinucleotide (NAD), AMP, and ADP-ribose supplied to intact human skin fibroblasts was monitored, and the concentrations 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 hydrolyzing the pyrophosphoric bond and yielding nicotinamide mononucleotide (nucleotide pyrophosphatase) and the other cleaving the glycoside link and releasing nicotinamide (NAD-glycohydrolase). No AMP or ADP-ribose was found in the extracellular medium of cells incubated with NAD, the former being completely catabolized to hypoxanthine and the latter degraded to adenine and hypoxanthine.