Nicotinamide adenine dinucleotide treatment confers resistance to neonatal ischemia and hypoxia:effects on neurobehavioral phenotypes

Neonatal hypoxic-ischemic brain injury is the main cause of hypoxic-ischemic encephalopathy and cerebral palsy.Currently,there are few effective clinical treatments for neonatal hypoxic-ischemic brain injury.Here,we investigated the neuroprotective and molecular mechanisms of exogenous nicotinamide adenine dinucleotide,which can protect against hypoxic injury in adulthood,in a mouse model of neonatal hypoxic-ischemic brain injury.In this study,nicotinamide adenine dinucleotide(5 mg/kg)was intraperitoneally administered 30 minutes befo re surgery and every 24 hours thereafter.The results showed that nicotinamide adenine dinucleotide treatment improved body weight,brain structure,adenosine triphosphate levels,oxidative damage,neurobehavioral test outcomes,and seizure threshold in experimental mice.Tandem mass tag proteomics revealed that numerous proteins were altered after nicotinamide adenine dinucleotide treatment in hypoxic-ischemic brain injury mice.Parallel reaction monitoring and western blotting confirmed changes in the expression levels of proteins including serine(or cysteine)peptidase inhibitor,clade A,member 3N,fibronectin 1,5'-nucleotidase,cytosolic IA,microtubule associated protein 2,and complexin 2.Proteomics analyses showed that nicotinamide adenine dinucleotide ameliorated hypoxic-ischemic injury through inflammation-related signaling pathways(e.g.,nuclear factor-kappa B,mitogen-activated protein kinase,and phosphatidylinositol 3 kinase/protein kinase B).These findings suggest that nicotinamide adenine dinucleotide treatment can improve neurobehavioral phenotypes in hypoxic-ischemic brain injury mice through inflammation-related pathways.

Nicotinamide adenine dinucleotide phosphate oxidase in pancreatic diseases:Mechanisms and future perspectives

Pancreatitis and pancreatic cancer(PC)stand as the most worrisome ailments affecting the pancreas.Researchers have dedicated efforts to unraveling the mechanisms underlying these diseases,yet their true nature continues to elude their grasp.Within this realm,oxidative stress is often believed to play a causal and contributory role in the development of pancreatitis and PC.Excessive accumulation of reactive oxygen species(ROS)can cause oxidative stress,and the key enzyme responsible for inducing ROS production in cells is nicotinamide adenine dinucleotide phosphate hydrogen oxides(NOX).NOX contribute to pancreatic fibrosis and inflammation by generating ROS that injure acinar cells,activate pancreatic stellate cells,and mediate macrophage polarization.Excessive ROS production occurs during malignant transformation and pancreatic carcinogenesis,creating an oxidative microenvironment that can cause abnormal apoptosis,epithelial to mesenchymal transition and genomic instability.Therefore,understanding the role of NOX in pancreatic diseases contributes to a more in-depth exploration of the exact pathogenesis of these diseases.In this review,we aim to summarize the potential roles of NOX and its mechanism in pancreatic disorders,aiming to provide novel insights into understanding the mechanisms underlying these diseases.

Effects of different concentrations of nicotinamide on hematopoietic stem cells cultured in vitro

BACKGROUND In vitro expansion to increase numbers of hematopoietic stem cells(HSCs)in cord blood could improve clinical efficacy of this vital resource.Nicotinamide(NAM)can promote HSC expansion ex vivo,but its effect on hematopoietic stem and progenitor cells(HSPCs,CD34^(+)CD38)and functional subtypes of HSCs-shortterm repopulating HSCs(ST-HSCs,CD34^(+)CD38CD45RACD49f^(+))and long-term repopulating HSCs(LT-HSCs,CD34^(+)CD38CD45RACD49f^(+)CD90^(+))is not yet known.As a sirtuin 1(SIRT1)inhibitor,NAM participates in regulating cell adhesion,polarity,migration,proliferation,and differentiation.However,SIRT1 exhibits dual effects by promoting or inhibiting differentiation in different tissues or cells.We propose that the concentration of NAM may influence proliferation,differentiation,and SIRT1 signaling of HSCs.AIM To evaluate the effects and underlying mechanisms of action of different concentrations of NAM on HSC proliferation and differentiation.METHODS CD34^(+)cells were purified from umbilical cord blood using MacsCD34 beads,and cultured for 10-12 d in a serum-free medium supplemented with cytokines,with different concentrations of NAM added according to experimental requirements.Flow cytometry was used to detect phenotype,cell cycle distribution,and apoptosis of the cultured cells.Real-time polymerase chain reaction was used to detect the transcription levels of target genes encoding stemness-related factors,che mokines,components of hypoxia pathways,and antioxidant enzymes.Dichloro-dihydro-fluorescein diacetate probes were used to evaluate intracellular production of reactive oxygen species(ROS).Determination of the effect of different culture conditions on the balance of cytokine by cytometric bead array.RESULTS Compared with the control group,the proportion and expansion folds of HSPCs(CD34^(+)CD38)incubated with 5 mmol/L or 10 mmol/L NAM were significantly increased(all P<0.05).The ST-HSCs ratio and fold expansion of the 5 mmol/L NAM group were significantly higher than those of the control and 10 mmol/L NAM groups(all P<0.001),whereas the LT-HSCs ratio and fold expansion of the 10 mmol/L NAM group were significantly higher than those of the other two groups(all P<0.05).When the NAM concentration was>10 mmol/L,cell viability significantly decreased.In addition,compared with the 5 mmol/L NAM group,the proportion of apoptotic cells in the 10 mmol/L NAM group increased and the proportion of cells in S and G2 phase decreased.Compared with the 5 mmol/L NAM group,the HSCs incubated with 10 mmol/L NAM exhibited significantly inhibited SIRT1 expression,increased intracellular ROS content,and downregulated expression of genes encoding antioxidant enzymes(superoxide dismutase 1,peroxiredoxin 1).CONCLUSION Low concentrations(5 mmol/L)of NAM can better regulate the balance between proliferation and differentiation,thereby promoting expansion of HSCs.These findings allow adjustment of NAM concentrations according to expansion needs.

Research Progress on the Application of β-Nicotinamide Mononucleotides in Cosmetics

Recent studies have found that nicotinamide mononucleotide(nicotinamide mononucleotide,NMN)also has certain anti-aging,photoprotection,anti-oxidation,and soothing to the skin,while affects the level of nicotinamide adenine dinucleotide(nicotinamide adenine dinucleotide,NAD+)to improve aging-related diseases.These skincare features have laid the foundation for its application in cosmetics.NMN has been used in cosmetics and sold on the market in foreign countries,but there have been debates about its safety.It is currently as a new raw material for cosmetics in China,and its safety is also under monitoring.This paper systematically reviewed the basic properties,skin care functions and the safety of its application in cosmetics,aiming to provide theoretical reference for the development and application of NMN.

Nicotinamide adenine dinucleotide phosphate oxidase activation and neuronal death after ischemic stroke

Nicotinamide adenine dinucleotide phosphate oxidase(NOX) is a multisubunit enzyme complex that utilizes nicotinamide adenine dinucleotide phosphate to produce superoxide anions and other reactive oxygen species. Under normal circumstances, reactive oxygen species mediate a number of important cellular functions, including the facilitation of adaptive immunity. In pathogenic circumstances, however,excess reactive oxygen species generated by NOX promotes apoptotic cell death. In ischemic stroke, in particular, it has been shown that both NOX activation and derangements in glucose metabolism result in increased apoptosis. Moreover, recent studies have established that glucose, as a NOX substrate, plays a vital role in the pathogenesis of reperfusion injury. Thus, NOX inhibition has the potential to mitigate the deleterious impact of hyperglycemia on stroke. In this paper, we provide an overview of this research,coupled with a discussion of its implications for the development of NOX inhibition as a strategy for the treatment of ischemic stroke. Both inhibition using apocynin, as well as the prospect of developing more specific inhibitors based on what is now understood of the biology of NOX assembly and activation, will be highlighted in the course of our discussion.

Effects of nicotinamide and riboflavin on the biodesulfurization activity of dibenzothiophene by Rhodococcus erythropolis USTB-03

Rhodococcus erythropolis USTB-03 is a promising bacterial strain for the biodesulfurization of dibenzothiophene （DBT） via a sulfurspecific pathway in which DBT is converted to 2-hydroxybiphenyl （2HBP） as an end product. The effects of nicotinamide and riboflavin on the sulfur specific activity （SA） of DBT biodesulfurization by R. erythropolis USTB-03 were investigated. Both nicotinamide and riboflavin were found to enhance the expression of SA, which was not previously reported. When R. erythropolis USTB-03 was grown on a medium containing nicotinamide of 10.0 mmol or riboflavin of 50.0 μmol, SA was raised from 68.0 or so to more than 130 mmol 2HBP/（kg dry cells.h）. When R. erythropolis USTB-03 was grown in the presence of both nicotinamide of 5.0 mmol and riboflavin of 25.0 μmol, SA was further increased to 159.0 mmol 2HBP/（kg dry cells.h）. It is suggested that the biological synthesis of reduced form of flavin mononucleotide （FMNH2）, an essential coenzyme for the activities of biodesulfurization enzyme Dsz C and A, might be enhanced by nicotinamide and riboflavin, which was responsible for the increased SA of R. erythropolis USTB-03.

Physiological Role of Humic Acid and Nicotinamide on Improving Plant Growth, Yield, and Mineral Nutrient of Wheat (<i>Triticum durum</i>) Grown under Newly Reclaimed Sandy Soil

Humic acid is not a fertilizer as it does not directly provide nutrients to plants, but is a compliment to fertilizer. Nicotinamide (Vitamin pp) is a stress-associated compound that can induce and regulate secondary metabolic accumulation and/or the manifestation of defense metabolism in plants. A field experiment was conducted at the experimental station of National Research center at El-Nubaria region, Egypt, to study the role of foliar application of humic acid (as soil conditioner 13 cm/l) and/or priming grains in nicotinamide (vitamin pp 5 mg/l) in saving irrigation water, decreasing fertilizer dose of NPK and at the same time increasing durum wheat (Triticum durum) cultivars’ (Beni Sweif-1 and Beni Sweif-3) productivity grown under newly reclaimed sandy soil exposed to drought for three weeks continuously. The results showed that plant treated with humic acid or nicotinamide increased significantly all morphological criteria (plant height, leaves number, fresh and dry weights of shoots), metabolism (photosynthetic pigment, total soluble sugar, total carbohydrates, total amino acids and proline), mineral contents (N, P, K, Ca and Mg) and yield (grain, straw and biology) of both cultivars amended with either recommended or half recommended doses of NPK. Foliar application of humic acid to plant priming in Vitamin pp induced significant increases in all studied parameters (morphology, chemical and yield) of plants amended with recommended or half recommended doses of NPK as compared with control plants. The maximum yields of grain, straw and biology of both cultivars were obtained in response to triple treatment (humic acid + nicotinamide + recommended dose of NPK) or (humic acid + nicotinamide + half recommended dose of NPK) respectively.

Nicotinamide mononucleotide supplementation improves the quality of porcine oocytes under heat stress

Background:Elevated ambient temperature-caused heat stress is a major concern for livestock production due to its negative impact on animal feed intake,growth,reproduction,and health.Particularly,the germ cells are extremely sensitive to the heat stress.However,the effective approach and strategy regarding how to protect mammalian oocytes from heat stress-induced defects have not been determined.Methods:Germinal vesicle(GV)porcine oocytes were cultured at 41.5℃ for 24 h to induce heat stress,and then cultured at 38.5℃ to the specific developmental stage for subsequent analysis.Nicotinamide mononucleotide(NMN)was dissolved in water to 1 mol/L for a stock solution and further diluted with the maturation medium to the final concentrations of 10μmol/L,20μmol/L,50μmol/L or 100μmol/L,respectively,during heat stress.Immunostaining and fluorescence intensity quantification were applied to assess the effects of heat stress and NMN supplementation on the key processes during the oocyte meiotic maturation.Results:Here,we report that NMN supplementation improves the quality of porcine oocytes under heat stress.Specifically,we found that heat stress resulted in oocyte maturation failure by disturbing the dynamics of meiotic organelles,including the cytoskeleton assembly,cortical granule distribution and mitochondrial function.In addition,heat stress induced the production of excessive reactive oxygen species(ROS)and DNA damage,leading to the occurrence of apoptosis in oocytes and subsequent embryonic development arrest.More importantly,we validated that supplementation of NMN during heat stress restored the meiotic defects during porcine oocyte maturation.Conclusions:Taken together,our study documents that NMN supplementation is an effective approach to improve the quality of oocytes under heat stress by promoting both nuclear and cytoplasmic maturation.

OTOTOXIC MODEL OF OXALIPLATIN AND PROTECTION FROM NICOTINAMIDE ADENINE DINUCLEOTIDE

Oxaliplatin, an anticancer drug commonly used to treat colorectal cancer and other tumors, has a number of serious side effects, most notably neuropathy and ototoxicity. To gain insights into its ototoxic profile, oxaliplatin was applied to rat cochlear organ cultures. Consistent with it neurotoxic propensity, oxaliplatin selectively damaged nerve fibers at a very low dose 1 μM. In contrast, the dose required to damage hair cells and spiral ganglion neurons was 50 fold higher (50 μM). Oxailiplatin-induced cochlear lesions initial-ly increased with dose, but unexpectedly decreased at very high doses. This non-linear dose response could be related to depressed oxaliplatin uptake via active transport mechanisms. Previous studies have demon-strated that axonal degeneration involves biologically active processes which can be greatly attenuated by nicotinamide adenine dinucleotide (NAD+). To determine if NAD+would protect spiral ganglion axons and the hair cells from oxaliplatin damage, cochlear cultures were treated with oxaliplatin alone at doses of 10 μM or 50 μM respectively as controls or combined with 20 mM NAD+. Treatment with 10 μM oxaliplatin for 48 hours resulted in minor damage to auditory nerve fibers, but spared cochlear hair cells. However, when cochlear cultures were treated with 10 μM oxaliplatin plus 20 mM NAD+, most auditory nerve fibers were intact. 50 μM oxaliplatin destroyed most of spiral ganglion neurons and cochlear hair cells with apop-totic characteristics of cell fragmentations. However, 50 μM oxaliplatin plus 20 mM NAD+treatment great-ly reduced neuronal degenerations and hair cell missing. The results suggested that NAD+provides signifi-cant protection against oxaliplatin-induced neurotoxicity and ototoxicity, which may be due to its actions of antioxidant, antiapoptosis, and energy supply.

Thermodynamics of Stability Constant of Binary Complex of Nicotinamide with Mn^(++)

The stability constants of the binary complexes of Mn2+ with nicotinamide (NA) were determined from potentiometric pH titrations data at 15.0 , 25.0 and 35.0oC and I = 0.1,0.2,0.4 mol L-1 (NaClO4). The formation of binary 1:1 , 1:2 NA-Mn complexes at three different temperatures and the influence of three different ionic strength on their stability were reported. The thermodynamic parameters (DGof, DSof, DHof) for the complex formation reaction were estimated from stability constant at different temperatures.

Synthesis and Crystal Structure of an Inclusion Compound Constructed through Self-assembly of Nicotinamide and Dicyanamide Coordination Bridges

A novel inclusion compound of [Mn（dca）2（3-nic）2]n·（3-nic）2n（1,dca = dicyanamide,3-nic = nicotinamide） has been prepared and characterized by single-crystal X-ray diffraction,elemental analysis and IR.This complex crystallizes in the triclinic system,space group P1 with a = 7.5979（8）,b = 7.7128（9）,c = 14.5346（17）,α = 100.094（2）,β = 92.444（2）,γ = 116.736（2）o,V = 741.72（15） 3,Z = 1,Dc = 1.512 g/cm3,Mr = 675.55,μ = 0.507 mm-1,F（000） = 347,S = 1.023,the final R = 0.0400 and wR = 0.1010.The inclusion compound is constructed by a three-dimensional host network that consists of dca,3-nic and Mn2＋ with coordination and hydrogen-bonding interactions.In the network,one-dimensional rectangular channels are formed,and the guest molecules（3-nic） are included in the channels.The guest molecules interlink with the host through strong hydrogen bonds.

Transcriptome analysis shows nicotinamide seed treatment alters expression of genes involved in defense and epigenetic processes in roots of seedlings of Picea abies

Nicotinamide treatment of plants and plant cell cultures has been shown to promote defense and decrease levels of DNA methylation.In the present study,we used RNA-seq technology to study overall changes in gene expression induced in roots of 3-month-old spruce(Picea abies)seedlings grown from nicotinamide-treated seeds to examine the molecular mechanisms underlying the defense promotion.Approximately 350 genes were identified as differentially expressed in roots after the seed treatment.Stress response genes,including transcription factors MYB77 and LHY and two chitinase enzymes,were generally upregulated,whereas genes thought to be involved in epigenetic regulation such as DDM1,known to promote DNA methylation,were present at high frequency among the downregulated genes.Across all samples,the expression of downregulated epigenetic-related genes was highly correlated with the nicotinamide treatment,indicating a common regulation.Our results support an earlier hypothesis regarding a potential role of nicotinamide as a defense-signal mediator.

Syntheses, Crystal Structures and Antitumor Activities of Two Nicotinamides

Two nicotinamides have been synthesized by coupling aromatic amines with equimolar quantities of substituted nicotinic acids. Their structures have been determined by X-ray single-crystal diffraction. Compound 1, 6-chloro-N-（4-fluorophenyl）nicotinamide, crystallizes in the triclinic space group Pī with a = 4.2188（8） , b = 5.0687（10）, c = 25.956（5）, α = 86.38（3）, β = 87.75（3）, γ = 83.20（3）°, V = 549.75（19） 3 and Z = 2. Compound 2, N-（quinolin-3-yl）nico- tinamide, crystallizes in the monoclinic space group P21 with a = 8.5100（17）, b = 6.4230（13）, c = 11.620（2） , β = 110.39（3）°, V = 595.3（2） 3 and Z = 2. The cytotoxic activities of the two nicotinamides against five human tumor cell lines were tested in vitro. The results indicated that they showed a wide range of antitumor activities.

Nicotinamide suppresses bevacizumab-induced epithelial-mesenchymal transition of ARPE-19 cells by attenuating oxidative stress

AIM:To investigate the effects of nicotinamide(NAM)on bevacizumab(BEV)-induced epithelial-mesenchymal transition(EMT)of human retinal pigment epithelial cells(ARPE-19)and the underling mechanisms.METHODS:ARPE-19 cells were treated with BEV for 24,48,and 72 h,and the variation degrees of EMTrelated markers(fibronectin,α-SMA,vimentin,and ZO-1)were assessed by Western blotting to select the optimal treatment time point which exhibited the most obvious changes of EMT-related markers for the subsequent experiments.Furthermore,NAM was added to the medium,the m RNA and protein levels of the EMT-related markers were then measured.The accumulation of reactive oxygen species(ROS)and H_(2)O_(2) and the total antioxidant capacity(TAC)of the cells were also measured to evaluate the level of oxidative stress.RESULTS:After being treated with BEV for 72 h,the protein expression levels of EMT-related markers in ARPE-19 cells showed significant changes.Meanwhile the levels of ROS and H_(2)O_(2) were obviously increased,and the TAC of ARPE-19 cells was decreased.Totally 72 h was chosen to be the optimal treatment time point in subsequentexperiments.Furthermore,NAM inhibited BEV-induced EMT by downregulating fibronectin,α-SMA,and vimentin and upregulating ZO-1,decreased the accumulation of ROS and H_(2)O_(2),and enhanced TAC in BEV-treated ARPE-19 cells.CONCLUSION:This study demonstrates that NAM suppressed BEV-induced EMT in ARPE-19 cells by attenuating oxidative stress.Hence,NAM may be a potential therapeutic agent for alleviating neovascular fibrosis of the ocular fundus after anti-vascular endothelial growth factor therapy.

Studies on Synthesis of Stationary Phase Containing Nicotinamide Adenine Dinucleotide(NAD) Bonded to Phospholipid-Coated Aminated Silica for HPLC

Recently biospecific affinity chromatography has been widely used for the separation and purification of various enzymes and nucleic acids. In this paper, a series of synthetic reactions of solid-liquid phase were carried out on silica surface, using a macroporous(30 mu m), microspherical silica (8 mu m) as the matrix and gamma-aminopropyltriethoxysilane as the activating agent, the nicotinamide adenine dinucleotide(NAD) was bonded through its amino groups to the carboxylic groups of linked phospholipid which was bonded covalently on aminated support. The bonded stationary phase has high thermal stability, and could be used to separate of nucleotides with good resolution.

Study of Tripterygium Associated with Nicotinamide in Treating Late-onset Autoimmune Diabetes Mellitus in Adults

Objective: To explore the effect of Tripterygium polyglycoside (TP) associated with nicotinamide on the islet cell function, immune parameters and lipoperoxide (LPO) in adult patients with late-onset autoimmune diabetes mellitus (LADA). Methods: Thirty-six cases of LADA were randomly divided into three groups: TP group (n=12), treated with TP plus orally taken metformin; combined treatment group (n= 12), treated with TP combined with nicotinamide and metformin, and control group (n=12) treated with metformin alone. They were followed-up for 18 months. Results: (1) Compared with the control group after 9 months of treatment, postprandial plasma glucose and LPO in combined treatment group were decreased (P <0.05), and the postprandial C-peptide was higher (P<0.05). At the 18th month, the value of postprandial C-peptide in the TP and combined treatment group was higher than that in the control group. The slL-2R level of both TP and combined treatment groups were lowered (P<0.01); (2) Islet cell antibody (ICA) positive of 5 cases in the TP group and 6 cases in the combined treatment group got converted to the negative respectively , while only one in the control group at the time (P<0.05); (3) The level of LPO in the combined treatment group was significantly lower than that in the TP group at the 18th month of treatment (P<0. 05). Conclusion: TP combined with nicotinamide played a role in immunity regulation, decreasing the titer of islet cell antibody and slL-2R, which also reduced the production of LPO and had a tendency to improve islet cell function in early LADA patients.

Nicotinamide Inhibition Properties for Copper Corrosion in 3.5% NaCl Solution: Experimental and Theorical Investigations

This work reports the inhibition properties of nicotinamide (NAM) for copper protection during its applications in seawater systems such as water pipelines, shipbuilding, seawater desalination and heat exchange systems. The efficiency of NAM as a copper corrosion inhibitor in simulated seawater (3.5% NaCl solution) was investigated by Tafel extrapolation and linear polarization methods in the temperature range from 20℃ to 50℃. The corrosion parameters and the adsorption isotherms were determined using potentiodynamic polarization techniques. It was found that the inhibition efficiency (η) and the coverage rate (θ) increase up 80% at 25℃ for nicotinamide concentration of 10 mM but decrease as the temperature of the solution increases. Moreover, the obtained thermodynamic parameters using Langmuir model suggested a physical adsorption type. A correlation was found between the corrosion inhibition efficiency and the global theoretical parameters obtained by the functional density method B3LYP/ 6-31 + G (d, p). Local parameters such as condensed Fukui functions [f(r)] and condensed local softness [s(r)] indices have also been determined to obtain a chemical insight into atoms that have a significant tendency toward donation or acceptance of whole or fraction of electrons.

SPECTROPHOTOMETRIC DETERMINATION OF N-HYDROXYMETHYL NICOTINAMIDE

A method for the determination of N-hydroxymethyl nicotinamide by spectrophotometry is described.N-hydroxymethyl nicotinamide was converted to acetate by acid-catalyzed acetylation,followed by base- catalyzed hydroxamation of the acetate ester and color development as the ferric hydroxamate chelate.The resulting colour solution was measured at 524nm,Beer's law is obeyed in the concentration range of 1--8x10^(-3) mol/L N- hydroxymethyl nicotinamide.

Nicotinamide Adenine Dinucleotide and Adenosine Triphosphate Oscillations Caused by Gradual Entry of Substrates within Mitochondria

Nicotinamide adenine dinucleotide (NAD) oscillation was observed when the isolated mitochondria were immersed in a pyruvate solution. In addition, when an adenosine diphosphate (ADP) was added to the mitochondrial suspension containing pyruvate, adenosine triphosphate (ATP) oscillation was observed as well as NADH oscillation. At this time, the pH within mitochondria also oscillated. It was found that the oscillatory reaction of NADH caused by the membrane permeation of pyruvate continues, causing the oscillation of NADH and H+ in the subsequent reactions. The pH oscillation led to the ATP oscillation. It is considered that the oscillatory reaction caused by the gradual entry of pyruvate into mitochondria was thought to be carried over to both the citric acid cycle and the respiratory chain, ultimately leading to the ATP oscillation in oxidative phosphorylation. Similarly, it was found that membrane permeation of malate causes the gradual occurrence of NADH, at which point NADH oscillates, followed by an oscillatory reaction of the respiratory chain, and finally ATP oscillation. It was found that the oscillations of NADH and ATP occur without going through the citric acid cycle. Oscillations of NADH and other intermediates in both the citric acid cycle and respiratory chain were also confirmed by experiments using semipermeable membranes. These results support our hypothesis that the gradual entry of the substrate by membrane permeation triggers an oscillatory reaction of the enzyme, which is also carried over to subsequent reactions.

Nicotinamide adenine dinucleotide(NAD^(+))reduction enabled by an atomically precise Au-Ag alloy nanocluster

The redox property of the ultrasmall coinage nanoclusters(with several to tens of Au/Ag atoms)has elucidated the electrontransfer capacity of nanoclusters,has been successfully utilized in a variety of redox conversions(such as from CO_(2)to CO).Nevertheless,their biological applications are mainly restricted by the scarcity of atomically precise,water-soluble metal nanoclusters,the limited application(mainly on the decomposition of H_(2)O_(2)in these days).Herein,mercaptosuccinic acid(MSA)protected ultrasmall alloy AuAg nanoclusters were prepared,the main product was determined[Au_(3)Ag_(5)(MSA)_(3)]−by electrospray ionization mass spectrometry(ESI-MS).The clusters can not only mediate the decomposition of H_(2)O_(2)to generate hydroxyl radicals,but is also able to mediate the reduction of nicotinamide adenine dinucleotide(NAD)to its reduced form of NADH.This is the first time that the atomically precise metal nanoclusters were used to mediate the coenzyme reduction.The preliminary mechanistic insights imply the reaction to be driven by the hydrogen bonding between the carboxylic groups(on the surface of MSA)and the amino N–H bonds(on NAD).In this context,the presence of the carboxylic groups,the sub-nanometer size regime(~1 nm),the synergistic effect of the Au-Ag clusters are pre-requisite to the NAD reduction.