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PubMed2001

Monitoring NAD(P)H autofluorescence to assess mitochondrial metabolic functions in rat hippocampal-entorhinal cortex slices.

Changes in neuronal energy metabolism, mitochondrial functions and homeostasis of reactive oxygen species are often supposed to induce alterations in neuronal activity in hippocampal slice models. In order to investigate the NAD(P)H autofluorescence signal in brain slice models, methods to monitor NAD(P)H signal in isolated mitochondria as described by Chance et al. [J. Biol. Chem. 254 (1979) 4764] and dissociated neurons as described by Duchen [Biochem. J. 283 (1992) 41] were adapted to recording conditions required for brain slices. Considering different experimental questions, we established an approach to monitor NAD(P)H autofluorescence signals from hippocampal slices of 400 microm thickness under either submerged or interface conditions. Therefore the procedure described here allows the measurement of NAD(P)H autofluorescence under conditions typically required in electrophysiological experiments. Depolarization of plasma membrane caused by electrical stimulation or application of glutamate (100 microM) resulted in a characteristic initial decrease followed by a long-lasting increase in the NAD(P)H autofluorescence signal. H(2)O(2) (100 microM) evoked a strong NAD(P)H signal decrease indicating direct oxidation to the nonfluorescencend NAD(P)(+). In contrast, the increase in NAD(P)H signal that followed a brief inhibition of mitochondrial respiratory chain complex I using rotenone (1 microM) indicated an accumulation of NAD(P)H. However, in presence of rotenone (1 microM) electrically evoked long-lasting NAD(P)H signal overshoot decreased progressively, due to a negative feedback of accumulated NAD(P)H to the citrate cycle. A comparable reduction in NAD(P)H signal increase were observed during low-Mg(2+) induced epileptiform activity, indicating a relative energy failure. In conclusion, the method presented here allows to monitor NAD(P)H autofluorescence signals to gain insight into the coupling of neuronal activity, energy metabolism and mitochondrial function in brain slice models.

Animals↗
PubMed2005

Molecular conversion of NAD kinase to NADH kinase through single amino acid residue substitution.

NAD kinase phosphorylates NAD+ to form NADP+ and is strictly specific to NAD+, whereas NADH kinase phosphorylates both NAD+ and NADH, thereby showing relaxed substrate specificity. Based on their primary and tertiary structures, the difference in the substrate specificities between NAD and NADH kinases was proposed to be caused by one aligned residue: Gly or polar amino acid (Gln or Thr) in five NADH kinases and a charged amino acid (Arg) in two NAD kinases. The substitution of Arg with Gly in the two NAD kinases relaxed the substrate specificity (i.e. converted the NAD kinases to NADH kinases). The substitution of Arg in one NAD kinase with polar amino acids also relaxed the substrate specificity, whereas substitution with charged and hydrophobic amino acids did not show a similar result. In contrast, the substitution of Gly with Arg in one NADH kinase failed to convert it to NAD kinase. These results suggest that a charged or hydrophobic amino acid residue in the position of interest is crucial for strict specificity of NAD kinases to NAD+, whereas Gly or polar amino acid residue is not the sole determinant for the relaxed substrate specificity of NADH kinases. The significance of the conservation of the residue at the position in 207 NAD kinase homologues is also discussed.

Amino Acid Sequence↗
PubMed1984

The binding of 1,N6-etheno-NAD to bovine liver glutamate dehydrogenase.

The binding of 1,N6-etheno-NAD (epsilon NAD) to bovine liver glutamate dehydrogenase (L-glutamate:NAD(P)+ oxidoreductase (deaminating), EC 1.4.1.3) saturated with glutarate has been investigated at pH 7.0, 0.05 M phosphate buffer at 20 degrees C, by fluorescence titrations. epsilon NAD binds to the protein in a simple fashion: one molecule of coenzyme per enzyme polypeptide chain in the range of enzyme concentrations investigated (from above 50 to a few micromoles of enzyme polypeptide chains/liter). The fluorescence enhancement factor, Q, of bound epsilon NAD relative to free epsilon NAD is independent of the saturation degree, as deduced from the constant value of the long fluorescence decay lifetime (about 21 ns), and is about 17, as deduced from Fmax/F0 ratio values obtained after extrapolation from double reciprocal plots of 1/delta F vs. 1/[glutamate dehydrogenase]. This value for the Q factor is also independent of enzyme concentration, as well as of the presence of either GTP or ADP. At low enzyme concentrations (below 20 mumol polypeptide chains/liter), the dissociation constant of epsilon NAD increases progressively from a plateau value of about 50 microM to about 100 microM at infinite dilution. This is interpreted as being due to a minor affinity of glutamate dehydrogenase hexamers, with respect to higher aggregation states of the enzyme, towards epsilon NAD. As expected, GTP and ADP change the affinity of glutamate dehydrogenase towards epsilon NAD in an opposite manner: GTP strongly increases it, whereas ADP strongly decreases it (Kappd around 6 microM with saturating GTP and around 300 microM with saturating ADP). Furthermore, in the case of GTP, both GTP and epsilon NAD bind to glutamate dehydrogenase with positive cooperativity, with a Hill coefficient of approx. 1.8 for both and a Kappd approximately equal to 30 microM for the binding of GTP to glutamate dehydrogenase saturated with epsilon NAD and glutarate. The value of the Q factor remains the same, even in the presence of the effectors (again from lifetime measurements), as well as the number of epsilon NAD binding sites per enzyme polypeptide chain. These results are interpreted in terms of independent active sites, in the case without effectors. With ADP the binding appears to be simple, but no careful investigation has been attempted at low enzyme concentrations because of the low saturation degree achievable, whereas with GTP the cooperativity can be explained as due to a shift towards hexamers from higher aggregation states.

Adenosine Diphosphate↗
PubMed2001

Bioorganometallic chemistry. 13. Regioselective reduction of NAD(+) models, 1-benzylnicotinamde triflate and beta-nicotinamide ribose-5'-methyl phosphate, with in situ generated [CpRh(Bpy)H](+): structure-activity relationships, kinetics, and mechanistic aspects in the formation of the 1,4-NADH derivatives.

Cofactor regeneration; i.e., regiospecific conversion of NAD(+) to 1,4-NADH, has been extensively studied and is a crucial component in the eventual use of 1,4-NADH in a variety of bioorganic synthesis processes involving the formation of chiral organic compounds. We have studied the reduction of a model NAD(+) compound, 1-benzylnicotinamide triflate, 1a, using [CpRh(bpy)(H(2)O)](2+), 2 (Cp = eta(5)-C(5)Me(5), bpy = 2,2'-bipyridyl), as the catalyst precursor and sodium formate (HCO(2)Na) as the hydride source in 1:1 H(2)O/THF and have found exclusive 1-benzyl-1,4-dihydronicotinamide regioselectivity, as was observed previously for natural NAD(+) that provided 1,4-NADH (see: Steckhan et al. Organometallics 1991, 10, 1568). Moreover, a variety of 3-substituted derivatives of 1-benzylpyridinium triflate, in addition to the -C(O)NH(2) group (1a), were also studied to ascertain that this 3-functionality (e.g., -C(O)NHCH(3), -C(S)NH(2), -C(O)CH(3), -C(O)OCH(3), and -CN, 1b,d-g) coordinates to a [CpRh(bpy)H](+) complex to direct the concerted, regioselective transfer of the hydride group from the rhodium to the 4-ring position of the NAD(+) model; all coordinating 3-substituents had relative rates in the 0.9-1.3 range with substrate 1a set to 1.0. If in fact the 3-substituent presented a steric effect [-C(O)NH(CH(2)CH(3))(2), 1c] or was a nonbinding group (-CH(3), 1h; -H, 1i), no catalytic hydride transfer was observed even with the more electrophilic 2 and 6 ring positions being readily available, which further implicated the crucial coordination of the NAD(+) model to the CpRh metal ion center. We also found that the 1-benzyl substituent on the nitrogen atom exerted a substantial electron-withdrawing effect, in comparison to the electron-donating 1-methyl substituent, and favorably affected the rate of the regioselective reduction (rate enhancement of 1-benzyl/1-methyl = 2.0). The kinetics of the regioselective reduction of 1a were studied to show that the initial rate of reduction, r(i), is affected by the concentrations of the substrate, 1a, precatalyst, 2, and the hydride source, HCO(2)Na, in 1:1 H(2)O/THF: d[1-benzyl-1,4-dihydronicotnamide]/dt = k(cat)[1a][2][HCO(2)Na]. Furthermore, we wish to demonstrate that a previously synthesized aqueous NAD(+) model, beta-nicotinamide ribose-5'-methyl phosphate, 3, shows a similar regioselectivity for the 1,4-NADH analogue, while the initial rate (r(i)) for the regioselective reduction of 3 and NAD(+) itself was found to be comparable in water but faster by a factor of approximately 3 in comparison to 1a in 1:1 H(2)O/THF; the solvent, THF, appeared to inhibit the rate of reduction in 1a by presumably competing with the substrate 1a for the CpRh metal ion center. However, in H(2)O, the initial kinetic rate for substrate 3 was not affected by its concentration and implies that, in H(2)O, [CpRh(bpy)H](+) formation is rate determining. We assume that binding of 3 and NAD(+) to the CpRh metal ion center is also a pertinent step for 1,4-dihydro product formation, the experimental rate expression in H(2)O being d[1,4-dihydro-beta-nicotinamide ribose-5'-methyl phosphate]/dt = k(cat)[2][HCO(2)Na]. What we have discovered, for the first time, is evidence that the regioselective reduction of NAD(+) to 1,4-NADH by [CpRh(bpy)H](+) is a consequence of the amide's ability to coordinate to the CpRh metal center, thereby constricting the kinetically favorable six-membered ring transition state for plausible concerted hydride transfer/insertion to C4 to regioselectively provide the 1,4-NADH derivative; [CpRh(bpy)H](+) can be categorized as a biomimetic enzymatic hydride via its ability to bind and regioselectively transfer hydride to C4, exclusively. Clearly, the pyrophosphate and adenosine groups associated with the structure of NAD(+) are not essential in the rate of hydride transfer to C4, with NAD(+) model 3 having a similar initial rate (r(i)) of reduction as NAD(+) itself in water. Finally, a catalytic cycle will be proposed to account for our overall observations.

Algorithms↗
PubMed2002

NAD binding induces conformational changes in Rho ADP-ribosylating clostridium botulinum C3 exoenzyme.

We have solved the crystal structures of Clostridium botulinum C3 exoenzyme free and complexed to NAD in the same crystal form, at 2.7 and 1.95 A, respectively. The asymmetric unit contains four molecules, which, in the free form, share the same conformation. Upon NAD binding, C3 underwent various conformational changes, whose amplitudes were differentially limited in the four molecules of the crystal unit. A major rearrangement concerns the loop that contains the functionally important ARTT motif (ADP-ribosyltransferase toxin turn-turn). The ARTT loop undergoes an ample swinging motion to adopt a conformation that covers the nicotinamide moiety of NAD. In particular, Gln-212, which belongs to the ARTT motif, flips over from a solvent-exposed environment to a buried conformation in the NAD binding pocket. Mutational experiments showed that Gln-212 is neither involved in NAD binding nor in the NAD-glycohydrolase activity of C3, whereas it plays a critical role in the ADP-ribosyl transfer to the substrate Rho. We observed additional NAD-induced movements, including a crab-claw motion of a subdomain that closes the NAD binding pocket. The data emphasized a remarkable NAD-induced plasticity of the C3 binding pocket and suggest that the NAD-induced ARTT loop conformation may be favored by the C3-NAD complex to bind to the substrate Rho. Our structural observations, together with a number of mutational experiments suggest that the mechanisms of Rho ADP-ribosylation by C3-NAD may be more complex than initially anticipated.

ADP Ribose Transferases↗
PubMed2003

The reported human NADsyn2 is ammonia-dependent NAD synthetase from a pseudomonad.

Nicotinamide-adenine dinucleotide (NAD+) synthetases catalyze the last step in NAD+ metabolism in the de novo, import, and salvage pathways that originate from tryptophan (or aspartic acid), nicotinic acid, and nicotinamide, respectively, and converge on nicotinic acid mononucleotide. NAD+ synthetase converts nicotinic acid adenine dinucleotide to NAD+ via an adenylylated intermediate. All of the known eukaryotic NAD+ synthetases are glutamine-dependent, hydrolyzing glutamine to glutamic acid to provide the attacking ammonia. In the prokaryotic world, some NAD+ synthetases are glutamine-dependent, whereas others can only use ammonia. Earlier, we noted a perfect correlation between presence of a domain related to nitrilase and glutamine dependence and then proved in the accompanying paper (Bieganowski, P., Pace, H. C., and Brenner, C. (2003) J. Biol. Chem. 278, 33049-33055) that the nitrilase-related domain is an essential, obligate intramolecular, thiol-dependent glutamine amidotransferase in the yeast NAD+ synthetase, Qns1. Independently, human NAD+ synthetase was cloned and shown to depend on Cys-175 for glutamine-dependent but not ammonia-dependent NAD+ synthetase activity. Additionally, it was claimed that a 275 amino acid open reading frame putatively amplified from human glioma cell line LN229 encodes a human ammonia-dependent NAD+ synthetase and this was speculated largely to mediate NAD+ synthesis in human muscle tissues. Here we establish that the so-called NADsyn2 is simply ammonia-dependent NAD+ synthetase from Pseudomonas, which is encoded on an operon with nicotinic acid phosphoribosyltransferase and, in some Pseudomonads, with nicotinamidase.

Amide Synthases↗
PubMed1987

Dynamics of NAD in cortical nephron segments: effect of nicotinamide and of dietary phosphate intake.

NAD content and the rate of NAD hydrolysis were determined in proximal convoluted tubules (PCT), proximal straight tubules (PST), and adjacent cortical nephron segments microdissected from kidneys of thyroparathyroidectomized (TPTX) rats. In the basal state, rats fed a normal phosphate diet had an NAD content higher in PCT, PST, and in cortical ascending limb (CAL) than in glomeruli. After intraperitoneal injection of nicotinamide, the NAD content increased significantly in all nephron segments except CAL; the greatest (delta + 277%) increase was found in PCT, with less (delta + 82%) in PST. In experiments conducted on TPTX rats stabilized on a low-phosphorus diet, NAD content increased in response to a nicotinamide injection in PCT (delta + 197%), but did not change significantly in PST. The catabolism of NAD was determined by generation of [3H]adenosine, a major metabolite of [adenine-2,8-3H]NAD. The rate of [3H]adenosine generation from [3H]NAD was significantly (P less than 0.001) higher in PST than in PCT. We conclude that, in response to nicotinamide administration in vivo, the NAD content increases more in PCT than in PST and that this difference may be, at least partly, due to a lower rate of NAD breakdown in PCT. In a state of dietary phosphate deprivation, NAD also increases significantly in response to intraperitoneal nicotinamide in PCT, but it does not increase significantly in PST. The nicotinamide-elicited increase of NAD content in proximal tubules, mainly in PCT, may be related to inhibition of Na+-gradient-dependent inorganic phosphate (Pi) reabsorption across the brush-border membrane of proximal tubules and to the phosphaturic effect of nicotinamide in rats fed normal-Pi diet.

Animals↗
PubMed2006

NAD+ and NADH in cellular functions and cell death.

Increasing evidence has indicated that NAD+ and NADH play critical roles not only in energy metabolism, but also in cell death and various cellular functions including regulation of calcium homeostasis and gene expression. It has also been indicated that NAD+ and NADH are mediators of multiple major biological processes including aging. NAD+ and NADH produce the biological effects by regulating numerous NAD+/NADH-dependent enzymes, including dehydrogenases, poly(ADP-ribose) polymerases, Sir2 family proteins (sirtuins), mono(ADP-ribosyl)transferases, and ADP-ribosyl cyclases. Of particular interest, NAD+-dependent generation of ADP-ribose, cyclic ADP-ribose and O-acetyl-ADP-ribose can mediate calcium homeostasis by affecting TRPM2 receptors and ryanodine receptors; and sirtuins and PARPs appear to play key roles in aging, cell death and a variety of cellular functions. It has also been indicated that NADH and NAD+ can be transported across plasma membranes of cells, and that extracellular NAD+ may be a new signaling molecule. Our latest studies have shown that intranasal NAD+ administration can profoundly decrease ischemic brain damage. These new pieces of information have fundamentally changed our understanding about NAD+ and NADH, suggesting novel paradigms about the metabolism and biological activities of NAD+ and NADH. Based on this information, it is tempted to hypothesize that NAD+ and NADH, together with ATP and Ca2+, may be four most fundamental components in life, which can significantly affect nearly all major biological processes. Future studies on NAD+ and NADH may not only elucidate some fundamental mysteries in biology, but also provide novel insights for interfering aging and many disease processes.

Cell Death↗
PubMed2007

NAD+ and NADH in brain functions, brain diseases and brain aging.

Numerous studies have suggested that NAD+ and NADH mediate multiple major biological processes, including calcium homeostasis, energy metabolism, mitochondrial functions, cell death and aging. In particular, NAD+ and NADH have emerged as novel, fundamental regulators of calcium homeostasis. It appears that most of the components in the metabolic pathways of NAD+ and NADH, including poly(ADP-ribose), ADP-ribose, cyclic ADP-ribose, O-acetyl-ADP-ribose, nicotinamide and kynurenine, can produce significant biological effects. This exquisiteness of NAD+ and NADH metabolism could epitomize the exquisiteness of life, through which we may grasp the intrinsic harmony life has evolved to produce. The exquisiteness also suggests a central regulatory role of NAD+ and NADH in life. It is tempted to propose that NAD+ and NADH, together with ATP and Ca2+, constitute a Central Regulatory Network of life. Increasing evidence has also suggested that NAD+ and NADH play important roles in multiple biological processes in brains, such as neurotransmission and learning and memory. NAD+ and NADH may also mediate brain aging and the tissue damage in various brain illnesses. Our latest studies have suggested that NADH can be transported across the plasma membranes of astrocytes, and that NAD+ administration can markedly decrease ischemic brain injury. Based on this information, it is proposed that NAD+ and NADH are fundamental mediators of brain functions, brain senescence and multiple brain diseases. Because numerous properties of NAD+ and NADH remain unclear, future studies regarding NAD+ and NADH may expose some fundamental mechanisms underlying brain functions, brain pathologies and brain aging.

Aging↗
PubMed1986

Anchimeric assistance in the intramolecular reaction of glucose-dehydrogenase-polyethylene glycol NAD conjugate.

Polyethylene glycol-bound derivatives of NAD(P) (PEG-NAD(P)) are water-soluble macromolecular coenzymes used in continuous enzyme reactors. These NAD(P) derivatives have good coenzyme activity for many dehydrogenases, but some enzymes such as glucose dehydrogenase (EC 1.1.1.47) show very low activity with these derivatives (less than 0.1% of that for native NAD(P)). In this work, we prepared a covalently linked glucose-dehydrogenase-polyethylene glycol-NAD conjugate (GlcDH-PEG-NAD) and found that the conjugate shows a much higher reaction rate than that of the native enzyme plus PEG-NAD: the ratio of the reaction rates of GlcDH-PEG-NAD and the native enzyme plus PEG-NAD is calculated to be 10,000-fold at the concentrations of the enzyme subunit and NAD moiety of 0.31 and 0.65 microM, respectively; the rate of the conjugate is even higher than that of the native enzyme plus native NAD. This rate acceleration is due to the increase in the effective concentration of NAD moiety ("anchimeric assistance") and demonstrates the potential of covalent linking for improving the interaction between an enzyme and a coenzyme derivative.

Bacillus megaterium↗
PubMed2003

Molecular identification of human glutamine- and ammonia-dependent NAD synthetases. Carbon-nitrogen hydrolase domain confers glutamine dependency.

NAD synthetase catalyzes the final step in the biosynthesis of NAD. In the present study, we obtained cDNAs for two types of human NAD synthetase (referred as NADsyn1 and NADsyn2). Structural analysis revealed in both NADsyn1 and NADsyn2 a domain required for NAD synthesis from ammonia and in only NADsyn1 an additional carbon-nitrogen hydrolase domain shared with enzymes of the nitrilase family that cleave nitriles as well as amides to produce the corresponding acids and ammonia. Consistent with the domain structures, biochemical assays indicated (i) that both NADsyn1 and NADsyn2 have NAD synthetase activity, (ii) that NADsyn1 uses glutamine as well as ammonia as an amide donor, whereas NADsyn2 catalyzes only ammonia-dependent NAD synthesis, and (iii) that mutant NADsyn1 in which Cys-175 corresponding to the catalytic cysteine residue in nitrilases was replaced with Ser does not use glutamine. Kinetic studies suggested that glutamine and ammonia serve as physiological amide donors for NADsyn1 and NADsyn2, respectively. Both synthetases exerted catalytic activity in a multimeric form. In the mouse, NADsyn1 was seen to be abundantly expressed in the small intestine, liver, kidney, and testis but very weakly in the skeletal muscle and heart. In contrast, expression of NADsyn2 was observed in all tissues tested. Therefore, we conclude that humans have two types of NAD synthetase exhibiting different amide donor specificity and tissue distributions. The ammonia-dependent synthetase has not been found in eucaryotes until this study. Our results also indicate that the carbon-nitrogen hydrolase domain is the functional domain of NAD synthetase to make use of glutamine as an amide donor in NAD synthesis. Thus, glutamine-dependent NAD synthetase may be classified as a possible glutamine amidase in the nitrilase family. Our molecular identification of NAD synthetases may prove useful to learn more of mechanisms regulating cellular NAD metabolism.

Amide Synthases↗
PubMed1996

NAD+ analogs substituted in the purine base as substrates for poly(ADP-ribosyl) transferase.

Poly(ADP-ribosyl) transferase (pADPRT) catalyzes the transfer of the ADP-ribose moiety from NAD+ onto proteins as well as onto protein-bound ADP-ribose. As a result, protein-bound polymers of ADP-ribose are formed. pADPRT itself contains several acceptor sites for ADP-ribose polymers and may attach polymers to itself (automodification). In this study the influence of substitutions in the purine base of NAD+ on the polymerization reaction was investigated. The adenine moiety of NAD+ was replaced by either guanine, hypoxanthine or 1,N6-ethenoadenine. These analogs served as substrates for polymer synthesis as judged from the extent of automodification of the enzyme and the sizes of the polymers formed. Time course experiments revealed that 1,N6-etheno NAD+ (epsilon-NAD+) and nicotinamide hypoxanthine dinucleotide (NHD+) were rather poor substrates as compared to NAD+. Synthesis of GDP-ribose polymers from nicotinamide guanine dinucleotide (NGD+) was more efficient, but still significantly slower than poly(ADP-ribosyl)ation of the enzyme using NAD+. The size of the different polymers appeared to correlate with these observations. After 30 min of incubation in the presence of 1 mM substrate, polymers formed from epsilon-NAD+ or NHD+ contained up to 30 epsilon-ADP-ribose or IDP-ribose units, respectively. Using NGD+ as substrate polymers consisted of more than 60 GDP-ribose units, an amount similar to that achieved by poly(ADP-ribosyl)ation in the presence of only 0.1 mM NAD+ as substrate. These results suggest that the presence of an amino group in the purine base of NAD+ may facilitate catalysis. Substitution of the nicotinamide moiety of NAD+ with 3-acetylpyridine had no detectable effect on polymer formation. Oligomers of GDP-ribose and epsilon-ADP-ribose exhibited a slower mobility in polyacrylamide gels as compared to ADP-ribose or IDP-ribose oligomers. This feature of the two former analogs as well as their markedly attenuated polymerization by pADPRT provide valuable tools for the investigation of the enzymatic mechanism of this protein. Moreover, polymers of epsilon-ADP-ribose may be useful for studying enzymes degrading poly(ADP-ribose) owing to the fluorescence of this analog. Digestion of epsilon-ADPR polymers with snake venom phosphodiesterase was accompanied by a significant fluorescence enhancement.

Adenosine Diphosphate Ribose↗
PubMed1991

Synthesis and properties of photoaffinity labels for the pyridine dinucleotide binding site of NAD glycohydrolase.

Two new photoactive analogues of oxidized nicotinamide adenine dinucleotide (NAD+) which are resistant to cleavage by NAD glycohydrolase were synthesized and characterized. The beta-D-ribonucleotide ring of the nicotinamide riboside moiety of NAD+ was replaced with a 2,3-dihydroxycyclopentane ring forming a carbocyclic dinucleotide analogue. Photoreactivity was achieved by the incorporation of an azido group at the 8-position of the adenosyl ring. The previously published synthesis of carbocyclic pyridine dinucleotide analogues [Slama, J. T., & Simmons, A. M. (1988) Biochemistry 27, 183] was modified by resolving the carbocyclic 1-aminoribose analogues and producing optically pure (+)-(1S)- or (-)-(1R)-4 beta-amino-2 alpha,3 alpha-dihydroxy-1 beta-cyclopentanemethanol. Each of these was converted to the corresponding carbocyclic nicotinamide 5'-nucleotide analogue and coupled with 8-azidoadenosine 5'-monophosphate. Two photoactive and isomeric NAD+ analogues were thus prepared. 8-Azidoadenosyl carba-NAD is the analogue in which D-dihydroxycyclopentane is substituted for the D-ribose of the nicotinamide nucleoside moiety. 8-Azido-adenosyl pseudocarba-NAD contains the L-carbocycle in place of the D-ribotide ring. 8-Azidoadenosyl carba-NAD was shown to inhibit the NAD glycohydrolase from Bungarus fasciatus venom competitively with an inhibitor dissociation constant of 187 microM. 8-Azidoadenosyl pseudocarba-NAD was shown to inhibit the same enzyme competitively with a Ki of 73 microM. The superior NADase inhibitor, 8-azidoadenosyl pseudocarba-NAD, was characterized kinetically and shown to fulfill the criteria required of a specific active site directed photoaffinity probe. Irradiation of mixtures of the photoprobe and NAD glycohydrolase with short-wave ultraviolet light resulted in the rapid and irreversible loss of enzyme activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Affinity Labels↗
PubMed1984

Intravesicular NAD has no effect on sodium-dependent phosphate transport in isolated renal brush border membrane vesicles.

The effects of intravesicular NAD on Na+-dependent 32Pi uptake were investigated in isolated rat kidney brush border membrane vesicles (BBMV). NAD was introduced into the vesicles by osmotic shock, and extravesicular NAD was removed by passing the vesicles through a anion exchange column. The effectiveness of the osmotic shock procedure and the hydrolysis of extra- and intravesicular NAD were controlled by enzymatic analysis and thin layer chromatography. ADP-ribosylation of the membrane proteins was analyzed in vesicles osmotically shocked in the presence of either [adenylate-32P]-NAD or [adenine-2,8-3H]-NAD by SDS-polyacrylamide gel electrophoresis. It was found that the Na+-dependent Pi uptake was inhibited when the BBMV were incubated with NAD at alkaline pH, which resulted in rapid NAD hydrolysis. When NAD was present in the intravesicular space only, the Na+-dependent Pi uptake was not inhibited. 32P from NAD was rapidly incorporated into a number of brush border membrane proteins, but no incorporation of 3H-adenine could be detected. The results provide evidence that NAD does not inhibit Pi transport by a direct interaction with the cytoplasmic side of the brush border membrane. No evidence of ADP-ribosylation of the brush border membrane protein(s) was found.

Animals↗
PubMed1980

Macromolecular derivatives of NAD and their application.

The effects of the properties of polymer chain and NAD density on the cofactor activity of polymeric NAD derivatives were investigated. NAD-N6- [N-(N-acryloyl-l-methoxycarbonyl-5-aminopentyl)-propioamide] (monomeric NAD derivative) was copolymerized with different kinds of vinyl monomers. The resulting polymeric NAD derivatives, except for that prepared with methacrylamide, had similar cofactor activities. These results show that the size and charge of the vinyl monomers do not have a great effect on the cofactor activity of polymeric NAD derivatives. The polymeric NAD derivative prepared by copolymerization with methacrylamide had the highest cofactor activities, and the activities for lactate and yeast alcohol dehydrogenases decreased with an increase in the NAD density of the polymer. These NAD density effects were mainly due to the inhibition by the polymeric NAD derivative with a high NAD density.

Alcohol Oxidoreductases↗
PubMed2001

Structure-function studies of human deoxyhypusine synthase: identification of amino acid residues critical for the binding of spermidine and NAD.

Deoxyhypusine synthase catalyses the first step in the biosynthesis of hypusine [N(epsilon)-(4-amino-2-hydroxybutyl)lysine]. The crystal structure of human deoxyhypusine synthase in complex with NAD revealed four NAD-binding sites per enzyme tetramer, and led to a prediction of the spermidine-binding pocket. We have replaced each of the seven amino acid residues at the predicted spermidine-binding site, and eleven residues that contact NAD, on an individual basis with alanine. Of the amino acid residues at the spermidine site, substitution of Asp-243, Trp-327, His-288, Asp-316 or Glu-323 with alanine caused an almost complete loss of spermidine binding and enzyme activity; only the mutation Tyr-305-->Ala showed partial binding and activity. His-288-->Ala was also deficient in terms of binding NAD. NAD binding was significantly reduced in all of the NAD-site mutant enzymes, except for Glu-137-->Ala, which showed a normal binding of NAD, but was totally lacking in spermidine binding. Of the NAD-site mutant enzymes, Asp-342-->Ala, Asp-313-->Ala and Asp-238-->Ala displayed the lowest binding of NAD. These enzymes and His-288Ala also showed a reduced binding of spermidine, presumably because spermidine binding is dependent on NAD. These findings permit the positive identification of amino acid residues critical for binding of spermidine and NAD, and provide a new insight into the complex molecular interactions involved in the deoxyhypusine synthase reaction.

Amino Acids↗
PubMed1993

Stimulation by nitric oxide of an NAD linkage to glyceraldehyde-3-phosphate dehydrogenase.

Nitric oxide-stimulated modification of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) by [adenylate-32P]NAD has been interpreted in recent reports as ADP-ribosylation. Incubations of GAPDH with the NO-releasing agent sodium nitroprusside (SNP) and NAD resulted, however, in essentially equal incorporation of radiolabel from the adenine, phosphate, and nicotinamide moieties to the extent of approximately 0.02 mol of NAD.mol of GAPDH-1. Modification of GAPDH by free adenosine 5'-diphosphoribose (ADP-ribose) was only 10% of that by NAD. Exposure of GAPDH modified by NAD in the presence of SNP to HgCl2, which acts at thiol linkages, released two products. Both contained nicotinamide and adenylate but did not cochromatograph with NAD. GAPDH activity was inhibited by SNP in a dose-dependent manner in the presence of NAD. When inhibition was 80%, with 1 mM SNP and 1 mM dithiothreitol, covalent modification with NAD was < 2%. This result is consistent with the conclusion that inhibition of GAPDH activity by SNP in the presence of NAD is due primarily to active-site nitrosylation, as reported by other workers, and is not due to the minor modification with NAD. These results demonstrate that NO-stimulated modification of GAPDH with NAD is not ADP-ribosylation as previously reported but rather is covalent binding of NAD through a NO-dependent thiol intermediate, possibly providing an example of an unexpected, altered reactivity of a nitrosylated protein.

Glyceraldehyde-3-Phosphate Dehydrogenases↗
PubMed2000

Cell-surface NAD(P)H-oxidase: relationship to trans-plasma membrane NADH-oxidoreductase and a potential source of circulating NADH-oxidase.

The surface of mammalian cells faces an oxidizing environment that has the potential to damage proteins, lipids, and carbohydrates to which it is exposed. In contrast, the cytoplasm is reducing and its redox state is tightly regulated. Trans-plasma membrane oxidoreductases that shift electrons from cytosolic NADH to external electron acceptors such as oxygen are widely involved in cellular redox control. They reduce oxygen to water and may generate reactive oxygen species such as superoxide and hydrogen peroxide. In addition, external NAD(P)H-oxidases have been demonstrated on intact cells and as eluted proteins, but the relationship between trans-plasma membrane NADH-oxidoreductases and cell-surface NAD(P)H-oxidases is not known. To investigate further the relationship between plasma membrane NAD(P)H-oxidoreductases, and to gain insight into the physiological functions of these redox active membrane proteins, we have adapted a simple colorimetric assay for measuring the trans-plasma membrane NADH-oxidoreductase activity of viable cells to measure NAD(P)H-oxidase at the cell surface in real time. Using the cell-impermeable tetrazolium salt WST-1 in the presence of NADH or NADPH, but in the absence of an intermediate electron acceptor, we show that cell-surface NAD(P)H-oxidase is widely expressed on mammalian cells, being more abundant on rapidly proliferating cells than on resting neutrophils and spleen cells. The ratio of cofactor dependence of NAD(P)H-oxidase (NADH:NADPH) varied widely between different cells (0.7-5.2), suggesting a family of cell surface oxidases or that the activity of these enzymes may be modulated in various ways. Comparison of NAD(P)H-oxidase on the surface of viable cells with trans-membrane NADH-oxidoreductase, measured with WST-1 in the presence of 1-methoxy PMS, showed that cell-surface NAD(P)H-oxidase was differentially inhibited by the cell-impermeable thiol-blocking agent pCMBS, but was unaffected or stimulated by other thiol blocking agents. Capsaicin, which inhibits trans-plasma membrane NADH-oxidoreductase activity, stimulated surface NAD(P)H-oxidase. Metabolic inhibitors had little effect on surface NAD(P)H-oxidase activity but inhibited trans-plasma membrane activity. These results do not support the view the surface NAD(P)H-oxidase is a terminal oxidase for trans-plasma membrane NADH-oxidoreductase.

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