Engineering of the thermophilic nitrile hydratase from Pseudonocardia thermophila JCM3095 for large-scale nicotinamide production based on sequence-activity relationships.

The green biocatalyst nitrile hydratase (NHase) is able to bio-transform 3-cyanopyridine into nicotinamide. As the NHase reaction is exothermic, an enzyme with high activity and stability is needed for nicotinamide production. In this study, we used sequence analysis and site-directed mutagenesis to generate a mutant of thermophilic NHase from Pseudonocardia thermophila JCM3095 with substantially enhanced activity and developed a powerful process for nicotinamide bio-production. The specific activity of αF126Y/αF168Y mutant was successfully increased by 3.98-fold over that of the wild-type enzyme. The half-life of such mutant was longer than 2 h, which was comparable to its parent enzyme. The relative activity of the αF126Y/αF168Y mutant after treatment with 1 M 3-cyanopyridine and 2 M nicotinamide was 73.2% and 63.7%, respectively, showing minor loss of its original stability. Structural analysis demonstrated that hydrogen bonds at the active site and α-ß subunit interface of the NHase contribute to the improved activity and the maintenance of stability. Escherichia coli transformant harboring the mutant NHase was used for nicotinamide bio-production, yielding a nicotinamide productivity of 251.1 g/(L·h), which is higher than the productivity obtained using other NHase-containing strains and transformants. The newly established variant is therefore a promising alternative for the industrial production of nicotinamides.

Nicotinamide mononucleotide production by fructophilic lactic acid bacteria.

Nicotinamide mononucleotide (NMN), an intermediate in nicotinamide adenine dinucleotide biosynthesis, is recently attracting much attention for its pharmacological and anti-aging efficacies. However, current commercial products containing NMN are very high-priced because efficient and facile methods for industrial NMN production are limited. In this study, aiming for its nutraceutical application, we attempted to screen lactic acid bacteria for intracellular and/or extracellular NMN production. Using a bioassay system with an auxotrophic yeast that requires nicotinamide riboside (NR; dephosphorylated NMN), three candidates were obtained from a library of 174 strains of facultative anaerobic lactic acid bacteria. All three candidates belonged to the genus Fructobacillus and produced NR in the culture media (0.8-1.5 mg/l). Lactic acid bacteria of the genus Fructobacillus are known to use D-fructose as an electron acceptor in anaerobic lactic acid fermentation; addition of D-fructose to the medium caused intracellular accumulation of NMN and NR, but no extracellular production of these compounds was observed. Draft genome sequencing for one of the candidates suggested that nicotinamide phosphoribosyltransferase, which exists commonly in mammals but is less reported in microorganisms, is a key enzyme for NMN and NR production in the fructophilic bacteria.

Creating enzymes and self-sufficient cells for biosynthesis of the non-natural cofactor nicotinamide cytosine dinucleotide.

Nicotinamide adenine dinucleotide (NAD) and its reduced form are indispensable cofactors in life. Diverse NAD mimics have been developed for applications in chemical and biological sciences. Nicotinamide cytosine dinucleotide (NCD) has emerged as a non-natural cofactor to mediate redox transformations, while cells are fed with chemically synthesized NCD. Here, we create NCD synthetase (NcdS) by reprograming the substrate binding pockets of nicotinic acid mononucleotide (NaMN) adenylyltransferase to favor cytidine triphosphate and nicotinamide mononucleotide over their regular substrates ATP and NaMN, respectively. Overexpression of NcdS alone in the model host Escherichia coli facilitated intracellular production of NCD, and higher NCD levels up to 5.0 mM were achieved upon further pathway regulation. Finally, the non-natural cofactor self-sufficiency was confirmed by mediating an NCD-linked metabolic circuit to convert L-malate into D-lactate. NcdS together with NCD-linked enzymes offer unique tools and opportunities for intriguing studies in chemical biology and synthetic biology.

Potential roles of gut microbiome and metabolites in modulating ALS in mice.

Amyotrophic lateral sclerosis (ALS) is a complex neurodegenerative disorder, in which the clinical manifestations may be influenced by genetic and unknown environmental factors. Here we show that ALS-prone Sod1 transgenic (Sod1-Tg) mice have a pre-symptomatic, vivarium-dependent dysbiosis and altered metabolite configuration, coupled with an exacerbated disease under germ-free conditions or after treatment with broad-spectrum antibiotics. We correlate eleven distinct commensal bacteria at our vivarium with the severity of ALS in mice, and by their individual supplementation into antibiotic-treated Sod1-Tg mice we demonstrate that Akkermansia muciniphila (AM) ameliorates whereas Ruminococcus torques and Parabacteroides distasonis exacerbate the symptoms of ALS. Furthermore, Sod1-Tg mice that are administered AM are found to accumulate AM-associated nicotinamide in the central nervous system, and systemic supplementation of nicotinamide improves motor symptoms and gene expression patterns in the spinal cord of Sod1-Tg mice. In humans, we identify distinct microbiome and metabolite configurations-including reduced levels of nicotinamide systemically and in the cerebrospinal fluid-in a small preliminary study that compares patients with ALS with household controls. We suggest that environmentally driven microbiome-brain interactions may modulate ALS in mice, and we call for similar investigations in the human form of the disease.

Structure-Based Engineering of Amidase from Pantoea sp. for Efficient 2-Chloronicotinic Acid Biosynthesis.

2-Chloronicotinic acid is a key intermediate of pharmaceuticals and pesticides. Amidase-catalyzed hydrolysis provides a promising enzymatic method for 2-chloronicotinic acid production from 2-chloronicotinamide. However, biocatalytic hydrolysis of 2-chloronicotinamide is difficult due to the strong steric and electronic effect caused by 2-position chlorine substituent of the pyridine ring. In this study, an amidase from a Pantoea sp. (Pa-Ami) was designed and engineered to have improved catalytic properties. Single mutant G175A and double mutant G175A/A305T strains exhibited 3.2- and 3.7-fold improvements in their specific activity for 2-chloronicotinamide, and the catalytic efficiency was significantly increased, with kcat/Km values 3.1 and 10.0 times higher than that of the wild type, respectively. Structure-function analysis revealed that the distance between Oγ of Ser177 (involved in the catalytic triad) and the carbonyl carbon of 2-chloronicotinamide was shortened in the G175A mutant, making the nucleophilic attack on the Oγ of Ser177 easier by virtue of proper orientation. In addition, the A305T mutation contributed to a suitable tunnel formation to facilitate the substrate entry and product release, resulting in improved catalytic efficiency. With the G175A/A305T double mutant as a biocatalyst, a maximum of 1,220 mM 2-chloronicotinic acid was produced with a 94% conversion, and the space-time yield reached as high as 575 gproduct liter-1 day-1 These results provide not only a novel robust biocatalyst for the production of 2-chloronicotinic acid but also new insights into amidase structure-function relationships.IMPORTANCE In recent years, the demand for 2-chloronicotinic acid has been greatly increased. To date, several chemical methods have been used for the synthesis of 2-chloronicotinic acid, but all include tedious steps and/or drastic reaction conditions, resulting in both economic and environmental issues. It is requisite to develop an efficient and green synthesis route. We recently screened Pa-Ami and demonstrated its potential for synthesis of 2-chloronicotinic acid from 2-chloronicotinamide. However, chlorine substitution on the pyridine ring of nicotinamide significantly affected the activity of Pa-Ami. Especially for 2-chloronicotinamide, the enzyme activity and catalytic efficiency were relatively low. In this study, based on structure-function analysis, we succeeded in engineering the amidase by structure-guided saturation mutagenesis. The engineered Pa-Ami exhibited quite high catalytic activity toward 2-chloronicotinamide and could serve as a promising biocatalyst for the biosynthesis of 2-chloronicotinic acid.

Organ Co-Relationship in Tryptophan Metabolism and Factors That Govern the Biosynthesis of Nicotinamide from Tryptophan.

The pathway of tryptophan (Trp)-nicotinamide is very important nutritionally because a vitamin nicotinamide is biosynthesized from an amino acid Trp. Until we started studying the factors that affect the Trp-nicotinamide conversion rate, little data existed. Data obtained from TDO (Trp 2,3-dioxygenase)-KO (knock-out) mice have revealed that mice can biosynthesize a necessary amount of nicotinamide from Trp by indoleamine 2,3-dioxygenase (IDO) even when TDO is lacking. It has also been shown that 3-hydroxyanthranilic acid is a key intermediate. Urine upper metabolites such as kynurenic acid and xanthurenic acid originate from non-hepatic tissues but not from the liver. Data obtained from quinolinic acid phosphoribosyltransferase (QPRT)-KO mice indicated that the Trp→quinolinic acid conversion ratio was 6%. Urine quinolinic acid levels and the conversion ratio of Trp to nicotinamide were the same between hetero and wild mice. These findings indicate that QPRT is not the rate-limiting enzyme in the conversion. Thus, the limiting factors in the conversion of Trp to nicotinamide are the amounts of 3-hydroxyanthranilic acid and quinolinic acid in the liver and the activity of liver 3-hydroxyanthranilic acid 3,4-dioxygenase. Studies on factors have shown that conversion of Trp to nicotinamide is increased by adequate intake of good quality protein, and adequate intake of unsaturated fatty acids and starch. However, conversion was decreased by deficient niacin, vitamin B2, or vitamin B6, excessive intake of protein, saturated fatty acids, or glucose and fructose, or intake of protein with low Trp content, and insufficient mineral intake.

Establishment of Bioprocess for Synthesis of Nicotinamide by Recombinant Escherichia coli Expressing High-Molecular-Mass Nitrile Hydratase.

Application of engineered bacteria expressing nitrile hydratase for the production of amide is getting tremendous attention due to the rapid development of recombinant DNA technique. This study evaluated the effect of 3-cyanopyridine concentrations on nicotinamide production using recombinant Escherichia coli strain (BAG) expressing high-molecular-mass nitrile hydratase from Rhodococcus rhodochrous J1, and established proper process of whole-cell catalysis of 3-cyanopyridine and high cell-density cultivation. The process of substrate fed-batch was applied in the production of nicotinamide, and the concentration of product reached 390 g/L under the condition of low cell-density. After the high cell-density cultivation of BAG in 5 L bioreactor, the OD600 of cell attained 200 and the total activity reached 2813 U/mL. Different high density of BAG after fermentation in the tank was used to catalyze 3-cyanopyridine, and the concentration of nicotinamide reached to 508 g/L in just 60 min. The productivity of BAG was 212% higher than that of R. rhodochrous J1, and it is possible that BAG is able to achieve industrial production of nicotinamide.

Vitamins B1, B2, B3 and B9 - Occurrence, Biosynthesis Pathways and Functions in Human Nutrition.

BACKGROUND: Vitamins are chemical compounds whose derivatives are involved in vital metabolic pathways of all living organisms. The complete endogenous biosynthesis of vitamins can be performed by many bacteria, yeast and plants, but humans need to acquire most of these essential nutrients with food. In recent years, new types of action of the well-recognized vitamins or their more sophisticated relationships have been reported. CONCLUSION: In this review we present the current knowledge of factors that can influence the yield and regulation of vitamin B1, B2, B3 and B9 biosynthesis in plants which can be important for human nutrition. A summary of modern methods applied for vitamin analysis in biological materials is also provided. Contributions of selected vitamins to the homeostasis of the human organism, as well as their relations to the progress or prevention of some important diseases such as cancer, cardiovascular diseases, diabetes and Alzheimer's disease are discussed in the light of recent investigations. Better understanding of the mechanisms of vitamin uptake by human tissues and possible metabolic or genetic backgrounds of vitamin deficiencies can open new perspectives on the medical strategies and biotechnological processes of food fortification.

Antitumor effect of combined NAMPT and CD73 inhibition in an ovarian cancer model.

Nicotinamide phosphoribosyltransferase (NAMPT) is a crucial enzyme in the biosynthesis of intracellular NAD+. NAMPT inhibitors have potent anticancer activity in several preclinical models by depleting NAD+ and ATP levels. Recently, we demonstrated that CD73 enables the utilization of extracellular NAD+/nicotinamide mononucleotide (NMN) by converting them to Nicotinamide riboside (NR), which can cross the plasmamembrane and fuel intracellular NAD+ biosynthesis in human cells. These processes are herein confirmed to also occur in a human ovarian carcinoma cell line (OVCAR-3), by means of CD73 or NRK1 specific silencing. Next, we investigated the anti-tumor activity of the simultaneous inhibition of NAMPT (with FK866) and CD73 (with α, ß-methylene adenosine 5'-diphosphate, APCP), in an in vivo human ovarian carcinoma model. Interestingly, the combined therapy was found to significantly decrease intratumor NAD+, NMN and ATP levels, compared with single treatments. In addition, the concentration of these nucleotides in ascitic exudates was more remarkably reduced in animals treated with both FK866 and APCP compared with single treatments. Importantly, tumors treated with FK866 in combination with APCP contained a statistically significant lower proportion of Ki67 positive proliferating cells and a higher percentage of necrotic area. Finally, a slight but significant increase in animal survival in response to the combined therapy, compared to the single agents, could be demonstrated. Our results indicate that the pharmacological inhibition of CD73 enzymatic activity could be considered as a means to potentiate the anti-cancer effects of NAMPT inhibitors.

Generation, Release, and Uptake of the NAD Precursor Nicotinic Acid Riboside by Human Cells.

NAD is essential for cellular metabolism and has a key role in various signaling pathways in human cells. To ensure proper control of vital reactions, NAD must be permanently resynthesized. Nicotinamide and nicotinic acid as well as nicotinamide riboside (NR) and nicotinic acid riboside (NAR) are the major precursors for NAD biosynthesis in humans. In this study, we explored whether the ribosides NR and NAR can be generated in human cells. We demonstrate that purified, recombinant human cytosolic 5'-nucleotidases (5'-NTs) CN-II and CN-III, but not CN-IA, can dephosphorylate the mononucleotides nicotinamide mononucleotide and nicotinic acid mononucleotide (NAMN) and thus catalyze NR and NAR formation in vitro. Similar to their counterpart from yeast, Sdt1, the human 5'-NTs require high (millimolar) concentrations of nicotinamide mononucleotide or NAMN for efficient catalysis. Overexpression of FLAG-tagged CN-II and CN-III in HEK293 and HepG2 cells resulted in the formation and release of NAR. However, NAR accumulation in the culture medium of these cells was only detectable under conditions that led to increased NAMN production from nicotinic acid. The amount of NAR released from cells engineered for increased NAMN production was sufficient to maintain viability of surrounding cells unable to use any other NAD precursor. Moreover, we found that untransfected HeLa cells produce and release sufficient amounts of NAR and NR under normal culture conditions. Collectively, our results indicate that cytosolic 5'-NTs participate in the conversion of NAD precursors and establish NR and NAR as integral constituents of human NAD metabolism. In addition, they point to the possibility that different cell types might facilitate each other's NAD supply by providing alternative precursors.

The kynurenine pathway activities in a sub-Saharan HIV/AIDS population.

BACKGROUND: Tryptophan is an essential amino acid for the synthesis of proteins and important metabolites such as serotonin, melatonin, tryptamine and niacin. After protein synthesis, more than 90 % of tryptophan catabolism occurs along the kynurenine pathway. The inflammation-inducible enzyme indoleamine 2,3 dioxygenase (IDO) is responsible for the first rate-limiting step in the kynurenine pathway, i.e., oxidation of tryptophan to kynurenine. Excessive IDO activity in conditions such as HIV/AIDS may lead to tryptophan depletion and accumulation of metabolites downstream from kynurenine. Little is known about the kynurenine pathway of HIV/AIDS patients in sub-Saharan regions. This study, in a low income sub-Saharan HIV/AIDS population, examined the effects of activities in the kynurenine pathway on plasma levels of tryptophan, kynurenine and the neurotoxin quinolinic acid, and on de novo synthesis of nicotinamide. METHODS: Plasma samples were obtained from a cohort of 105 HIV patients and 60 controls. Kynurenine pathway metabolites were analysed using gas chromatography - mass spectrometry. ELISA and flow cytometry were used to assess plasma inflammatory markers. RESULTS: IDO activity, depletion of tryptophan, as well as accumulation of kynurenine and the neurotoxin quinolinic acid, were not only significantly greater in the patients than in the controls, but also markedly greater than in HIV/AIDS patients from developed countries. Tryptophan levels were 12.3 % higher, kynurenine levels 16.2 % lower, quinolinic acid levels 43.2 % lower and nicotinamide levels 27,2 % lower in patients on antiretroviral treatment than in antiretroviral-naïve patients. Patients' kynurenine pathway metabolites correlated with the levels of inflammatory markers, including that of the major IDO-inducer, interferon-gamma. Indications are that the rate of de novo synthesis of nicotinamide in the kynurenine pathway correlates with increases in quinolinic acid levels up to a point where saturation of the enzyme quinolinate phosphoribosyl transferase occurs. CONCLUSIONS: Higher levels of inflammatory activity in this low income sub-Saharan HIV/AIDS population than in patients from developed countries lead to greater tryptophan depletion and greater accumulation of metabolites downstream from tryptophan with quinolinic acid levels often reaching levels associated with the development of HIV/AIDS-associated neurocognitive dysfunction. De novo synthesis of nicotinamide from quinolinic acid contributes to the maintenance of nicotinamide, and by implication NAD levels, in HIV/AIDS patients from low income populations. Antiretroviral treatment partially corrects disturbances in the kynurenine pathway.

Strategies for regeneration of nicotinamide coenzymes emphasizing self-sufficient closed-loop recycling systems.

Biocatalytic reduction reactions depending on nicotinamide coenzymes require an additional reaction to regenerate the consumed cofactor. For preparative application the preferred method is the simultaneous coupling of an in situ regeneration reaction. There are different strategically advantageous routes to achieve this goal. The standard method uses a second enzyme and a second co-substrate, for example formate and formate dehydrogenase or glucose and glucose dehydrogenase. Alternatively, a second substrate is employed which is converted by the same enzyme used for the primary reaction. For example, alcohol dehydrogenase catalyzed reactions are often coupled with excess 2-propanol which is oxidized to acetone during the regeneration of NAD(P)H. A third method utilizes a reaction-internal sequence by the direct coupling of an oxidizing and a reducing enzyme reaction. Neither an additional substrate nor a further regenerating enzyme are required for the recycling reaction. This kind of "closed-loop" or "self-sufficient" redox process for cofactor regeneration has been used rarely so far. Its most intriguing advantage is that even redox reactions with unstable precursors can be realized provided that this compound is produced in situ by an opposite redox reaction. This elegant method is applicable in special cases only but increasing numbers of examples have been published during the last years.

Contributions of tryptophan 2,3-dioxygenase and indoleamine 2,3-dioxygenase to the conversion of D-tryptophan to nicotinamide analyzed by using tryptophan 2,3-dioxygenase-knockout mice.

We investigated the contribution percentage of tryptophan 2,3-dioxygenase (TDO) and indoleamine 2,3-dioxygenase (IDO) to the conversion of D-tryptophan to nicotinamide in TDO-knockout mice. The calculated percentage conversions indicated that TDO and IDO oxidized 70 and 30%, respectively, of the dietary L-tryptophan. These results indicate that both TDO and IDO biosynthesize nicotinamide from D-tryptophan and L-tryptophan in mice.

The niacin required for optimum growth can be synthesized from L-tryptophan in growing mice lacking tryptophan-2,3-dioxygenase.

In mammals, nicotinamide (Nam) is biosynthesized from l-tryptophan (l-Trp). The enzymes involved in the initial step of the l-Trp→Nam pathway are l-Trp-2,3-dioxygenase (TDO) and indoleamine-2,3-dioxygenase (IDO). We aimed to determine whether tdo-knockout (tdo(-/-)) mice fed a diet without preformed niacin can synthesize enough Nam to sustain optimum growth. Wild-type (WT) and tdo(-/-) mice were fed a chemically defined 20% casein diet with or without preformed niacin (30 mg nicotinic acid/kg) for 28 d. Body weight, food intake, and liver NAD concentrations did not differ among the groups. In the groups of mice fed the niacin-free diet, urinary concentrations of the upstream metabolites kynurenine (320% increase, P < 0.0001), kynurenic acid (270% increase, P < 0.0001), xanthurenic acid (770% increase, P < 0.0001), and 3-hydroxyanthranilic acid (3-HA; 450% increase, P < 0.0001) were higher in the tdo(-/-) mice than in the WT mice, while urinary concentrations of the downstream metabolite quinolinic acid (QA; 50% less, P = 0.0010) and the sum of Nam and its catabolites (10% less, P < 0.0001) were lower in the tdo(-/-) mice than in the WT mice. These findings show that the kynurenine formed in extrahepatic tissues by IDO and subsequent enzymes can be metabolized up to 3-HA, but not into QA. However, the tdo(-/-) mice sustained optimum growth even when fed the niacin-free diet for 1 mo, suggesting they can synthesize the minimum necessary amount of Nam from l-Trp, because the liver can import blood kynurenine formed in extrahepatic tissues and metabolize it into Nam via NAD and the resulting Nam is then distributed back into extrahepatic tissues.

Recycling nicotinamide. The transition-state structure of human nicotinamide phosphoribosyltransferase.

Human nicotinamide phosphoribosyltransferase (NAMPT) replenishes the NAD pool and controls the activities of sirtuins, mono- and poly-(ADP-ribose) polymerases, and NAD nucleosidase. The nature of the enzymatic transition-state (TS) is central to understanding the function of NAMPT. We determined the TS structure for pyrophosphorolysis of nicotinamide mononucleotide (NMN) from kinetic isotope effects (KIEs). With the natural substrates, NMN and pyrophosphate (PPi), the intrinsic KIEs of [1'-(14)C], [1-(15)N], [1'-(3)H], and [2'-(3)H] are 1.047, 1.029, 1.154, and 1.093, respectively. A unique quantum computational approach was used for TS analysis that included structural elements of the catalytic site. Without constraints (e.g., imposed torsion angles), the theoretical and experimental data are in good agreement. The quantum-mechanical calculations incorporated a crucial catalytic site residue (D313), two magnesium atoms, and coordinated water molecules. The TS model predicts primary (14)C, α-secondary (3)H, ß-secondary (3)H, and primary (15)N KIEs close to the experimental values. The analysis reveals significant ribocation character at the TS. The attacking PPi nucleophile is weakly interacting (r(C-O) = 2.60 Å), and the N-ribosidic C1'-N bond is highly elongated at the TS (r(C-N) = 2.35 Å), consistent with an A(N)D(N) mechanism. Together with the crystal structure of the NMN·PPi·Mg2·enzyme complex, the reaction coordinate is defined. The enzyme holds the nucleophile and leaving group in relatively fixed positions to create a reaction coordinate with C1'-anomeric migration from NAM to the PPi. The TS is reached by a 0.85 Å migration of C1'.

Dietary quinic acid supplied as the nutritional supplement AIO + AC-11® leads to induction of micromolar levels of nicotinamide and tryptophan in the urine.

Hippuric acid is synthesized and produced primarily by the gastrointestinal (GI) microflora. However, there is no known health benefit for hippuric acid except its catabolic conjugation of benzene-type compounds via glycine and subsequent excretion in the urine. For years the GI tract microflora were known to metabolize quinic acid to hippuric acid. Recently it was also proposed that DNA repair was strongly enhanced by quinic acid. In order to explain these quinic acid effects, Pero and colleagues have examined whether tryptophan and nicotinamide were also enhanced by quinic acid levels in urine. They were indeed, and so another study was designed using a natural supplement source of quinic acid called AIO + AC-11®, and then the effects of intervention were measured after only 21 days. It was possible to show profound increases in quinic acid that were again paralleled by increases in tryptophan and nicotinamide urinary levels. Because the high pressure liquid chromatography (HPLC) methods differed greatly between the two studies, differences in chemical analyses probably did not contribute to the data base.

NADH oxidase activity of Bacillus subtilis nitroreductase NfrA1: insight into its biological role.

NfrA1 nitroreductase from the Gram-positive bacterium Bacillus subtilis is a member of the NAD(P)H/FMN oxidoreductase family. Here, we investigated the reactivity, the structure and kinetics of NfrA1, which could provide insight into the unclear biological role of this enzyme. We could show that NfrA1 possesses an NADH oxidase activity that leads to high concentrations of oxygen peroxide and an NAD(+) degrading activity leading to free nicotinamide. Finally, we showed that NfrA1 is able to rapidly scavenge H(2)O(2) produced during the oxidative process or added exogenously.

A continuous microplate assay for sirtuins and nicotinamide-producing enzymes.

Nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylases (sirtuins) and other enzymes that produce nicotinamide are integral to many cellular processes. Yet current activity measurements involve expensive and time-consuming assays. Here we present a spectroscopic assay that circumvents many issues of previous methods. This assay permits continuous product monitoring over time, allows determination of steady-state kinetic parameters, and is readily adaptable to high-throughput screening. The methodology uses an enzyme-coupled system in which nicotinamide is converted to nicotinic acid and ammonia by nicotinamidase. The ammonia is transferred to alpha-ketoglutarate via glutamate dehydrogenase, yielding glutamate and the oxidation of NAD(P)H to NAD(P)+, which is measured spectrophotometrically at 340 nm. Using this continuous assay with sirtuin-1 (Sirt1) and the ADP-ribosyl cyclase CD38, the resulting steady-state kinetic parameters are in excellent agreement with values obtained by other published methods. Importantly, this assay permitted determination of k(cat) and K(m) values with the native acetylated substrate acetyl-CoA synthetase-1; measurement of Sirt1, Sirt2, and Sirt3 activities from mammalian cell extracts; and determination of IC(50) values of various Sirt1 inhibitors. This assay is applicable to any nicotinamide-forming enzyme and will be an important tool to address many outstanding questions surrounding their regulation.

Production of L-tryptophan-derived catabolites in hepatocytes from streptozotocin-induced diabetic rats.

BACKGROUND: Recently the L-tryptophan (Trp) metabolites such as L-kynurenine(Kyn), L-kinurenic acid, quinolinic acid (QA) and picolinic acid (PA) have been shown physiologically important in central nervous and immune system, and various enzyme activities concerning their production were reported to be affected by insulin-dependent diabetes mellitus. However, the states of these metabolites in diabetes have not been clarified enough yet. AIM OF STUDY: The present study was performed to make clear the states of the productions of L-Kyn, QA, PA and nicotinamide (Nam) in vitro in the hepatocytes prepared from streptozotocin (STZ)-induced diabetic rats using [5-3H]L-Trp. METHODS: The diabetic model rats were made by STZ injection (60 mg/kg) and the hepatocytes isolated from the rats were incubated with [5-3H]L-Trp. The amounts of metabolites derived from L-Trp were determined by the isotope-dilution methods. RESULTS: The alpha-amino-beta-carboxymuconate-epsilon-semiarldehyde decarboxylase (ACMSD) mRNA level in the diabetic group was greatly higher than that in the control group. In the STZ-induced diabetes group, the amount of [5-3H]L-Trp converted to tritiated water, L-Kyn or QA were found to be more than 3 times of that in the control group, respectively. The produced amounts of PA and Nam were not significantly different between the diabetic and the control groups. CONCLUSIONS: It is suggested that STZ-diabetes mellitus causes augmentations of both L-Kyn and QA generations but not those of PA and Nam in liver, indicating the possibility that the immune and neuronal systems of insulin dependent diabetes mellitus would be influenced by the increased amounts of LKyn and QA but not by those of PA and Nam.

Antioxidant metabolism induced by quinic acid. Increased urinary excretion of tryptophan and nicotinamide.

For over 50 years, hippuric/quinic acids were believed to have no biological efficacy. Here data are presented to support the hypothesis that quinic acid is not responsible for any efficacy, but rather that quinic acid nutritionally supports the synthesis of tryptophan and nicotinamide in the gastrointestinal (GI) tract, and that this in turn leads to DNA repair enhancement and NF-kB inhibition via increased nicotinamide and tryptophan production.Moreover, it is shown that quinic acid is a normal constituent of our diet, capable of conversion to tryptophan and nicotinamide via the GI tract microflora, thus providing an in situ physiological source of these essential metabolic ingredients to humans. The concentrations of quinic and hippuric acids in the diet were dependent on each other when analysed in urine, as was evidenced by a significant linear regression analysis that included unsupplemented control subjects (n = 45, p < 0.001). Thus, these ingredients were identified as major dietary components, and not simply originating from environmental pollution as previously had been thought.