Transport of reduced nicotinamide-adenine dinucleotide into mitochondria of rat white adipose tissue.
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ABSTRACT:
SUBMITTER: Robinson BH
PROVIDER: S-EPMC1185350 | biostudies-other | 1970 Jan
REPOSITORIES: biostudies-other
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Project description:Mitochondrial NAD levels influence fuel selection, circadian rhythms, and cell survival under stress. It has alternately been argued that NAD in mammalian mitochondria arises from import of cytosolic nicotinamide (NAM), nicotinamide mononucleotide (NMN), or NAD itself. We provide evidence that murine and human mitochondria take up intact NAD. Isolated mitochondria preparations cannot make NAD from NAM, and while NAD is synthesized from NMN, it does not localize to the mitochondrial matrix or effectively support oxidative phosphorylation. Treating cells with nicotinamide riboside that is isotopically labeled on the nicotinamide and ribose moieties results in the appearance of doubly labeled NAD within mitochondria. Analogous experiments with doubly labeled nicotinic acid riboside (labeling cytosolic NAD without labeling NMN) demonstrate that NAD(H) is the imported species. Our results challenge the long-held view that the mitochondrial inner membrane is impermeable to pyridine nucleotides and suggest the existence of an unrecognized mammalian NAD (or NADH) transporter.
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Project description:1. The concentrations of NADP and NADPH(2) in homogenates of rat liver (expressed as mug./g. wet wt. of tissue homogenized) were compared with values obtained from intact samples of liver taken from the same female rat. With 0.25m-sucrose alone as the suspending medium, or in combination with tris buffer or 0.01-0.1m-nicotinamide, considerable decreases in the sum of the NADP+NADPH(2) concentrations were occasionally observed during 30min. storage of homogenates at 0 degrees . However, addition of 0.5m-nicotinamide+5mm-tris buffer to 0.25m-sucrose for use as a suspending medium maintained the sum of the NADP+NADPH(2) concentrations in homogenates at the level found in intact tissue for at least 30min. at 0 degrees . 2. The effects of freezing intact tissue and homogenates in liquid nitrogen before the extraction of NADP and NADPH(2) were studied. Freezing alone appears to convert a significant amount (approx. 30%) of liver NADPH(2) into an equivalent amount of NADP in intact tissue. This is discussed in terms of the ;bound NADP' reported by Burch, Lowry & Von Dippe (1963). 3. The intracellular distributions of NADP and NADPH(2) in intracellular fractions of rat liver were studied by using a modified centrifuging scheme that allows extraction of the isolated fractions to be performed within 45min. of killing the animal. Approx. 50% of the total NADP+NADPH(2) was found in the large-particle fractions and the remaining 50% was mostly in the soluble fraction of the cell. 4. Further investigations are reported on the nature of ;bound NADP' in rat liver. Most of this material appears associated with the ;nuclear' (containing nuclei, debris, erythrocytes etc.) or large-mitochondrial fractions, or both, obtained by low-speed centrifuging of rat-liver homogenates. 5. Although in some experiments the variations produced in the concentration of NADPH(2) present in large-particle fractions were followed by similar changes in that of ;bound NADP', in other cases no such direct relationship was obtained. Addition of phenazine methosulphate, for example, consistently lowered the concentration of NADPH(2) yet raised the concentration of ;bound NADP' in rat-liver mitochondrial fractions.
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Project description:Nicotinamide adenine dinucleotide (NAD+) is a key redox compound in all living cells responsible for energy transduction, genomic integrity, life-span extension, and neuromodulation. Here, we report a new function of NAD+ as a molecular photocatalyst in addition to the biological roles. Our spectroscopic and electrochemical analyses reveal light absorption and electronic properties of two π-conjugated systems of NAD+. Furthermore, NAD+ exhibits a robust photostability under UV-Vis-NIR irradiation. We demonstrate photocatalytic redox reactions driven by NAD+, such as O2 reduction, H2O oxidation, and the formation of metallic nanoparticles. Beyond the traditional role of NAD+ as a cofactor in redox biocatalysis, NAD+ executes direct photoactivation of oxidoreductases through the reduction of enzyme prosthetic groups. Consequently, the synergetic integration of biocatalysis and photocatalysis using NAD+ enables solar-to-chemical conversion with the highest-ever-recorded turnover frequency and total turnover number of 1263.4 hour-1 and 1692.3, respectively, for light-driven biocatalytic trans-hydrogenation.
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Project description:The regenerative capacity of the liver is essential for recovery from surgical resection or injuries induced by trauma or toxins. During liver regeneration, the concentration of nicotinamide adenine dinucleotide (NAD) falls, at least in part due to metabolic competition for precursors. To test whether NAD availability restricts the rate of liver regeneration, we supplied nicotinamide riboside (NR), an NAD precursor, in the drinking water of mice subjected to partial hepatectomy. NR increased DNA synthesis, mitotic index, and mass restoration in the regenerating livers. Intriguingly, NR also ameliorated the steatosis that normally accompanies liver regeneration. To distinguish the role of hepatocyte NAD levels from any systemic effects of NR, we generated mice overexpressing nicotinamide phosphoribosyltransferase, a rate-limiting enzyme for NAD synthesis, specifically in the liver. Nicotinamide phosphoribosyltransferase overexpressing mice were mildly hyperglycemic at baseline and, similar to mice treated with NR, exhibited enhanced liver regeneration and reduced steatosis following partial hepatectomy. Conversely, mice lacking nicotinamide phosphoribosyltransferase in hepatocytes exhibited impaired regenerative capacity that was completely rescued by administering NR.ConclusionNAD availability is limiting during liver regeneration, and supplementation with precursors such as NR may be therapeutic in settings of acute liver injury. (Hepatology 2017;65:616-630).
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Project description:In this work, we for the first time report the identification of UV filters in the bird eye lens. We found that lenses of some raptors (black kite, common buzzard) and waterfowl (birds from Podicipedidae family) contain unusually high levels of reduced nicotinamide adenine dinucleotide (NADH)—a compound with high absorption in the UV-A range with a maximum at 340 nm. The lens metabolome of these birds also features an extremely low [NAD +]/[NADH] ratio. Chemometric analysis demonstrates that the differences between the metabolomic compositions of lenses with low and high NADH abundances should be attributed to the taxonomic features of bird species rather to the influence of the low [NAD +]/[NADH] ratio. We attributed this observation to the low metabolic activity in lens fiber cells, which make up the bulk of the lens tissue. Photochemical measurements show that properties of NADH as a UV filter are as good as that of UV filters in the human lens, including strong absorption in the UV-A spectral region, high photostability under both aerobic and anaerobic conditions, low yields of triplet state, fluorescence, and radicals under irradiation. Lenticular UV filters protect the retina and the lens from photo-induced damages and improve the visual acuity by reducing chromatic aberrations; therefore, the results obtained contribute to our understanding of the extremely high acuity of the raptor vision.
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Project description:Universal and ubiquitous redox cofactors, nicotinamide adenine dinucleotide (NAD) and its phosphorylated analog (NADP), collectively contribute to approximately 12% of all biochemical reactions included in the metabolic model of Escherichia coli K-12. A homeostasis of the NAD pool faithfully maintained by the cells results from a dynamic balance in a network of NAD biosynthesis, utilization, decomposition, and recycling pathways that is subject to tight regulation at various levels. A brief overview of NAD utilization processes is provided in this review, including some examples of nonredox utilization. The review focuses mostly on those aspects of NAD biogenesis and utilization in E. coli and Salmonella that emerged within the past 12 years. The first pyridine nucleotide cycle (PNC) originally identified in mammalian systems and termed the Preiss-Handler pathway includes a single-step conversion of niacin (Na) to NaMN by nicotinic acid phosphoribosyltransferase (PncB). In E. coli and many other prokaryotes, this enzyme, together with nicotinamide deamidase (PncA), compose the major pathway for utilization of the pyridine ring in the form of amidated (Nm) or deamidated (Na) precursors. The existence of various regulatory mechanisms and checkpoints that control the NAD biosynthetic machinery reflects the importance of maintaining NAD homeostasis in a variety of growth conditions. Among the most important regulatory mechanisms at the level of individual enzymes are a classic feedback inhibition of NadB, the first enzyme of NAD de novo biosynthesis, by NAD and a metabolic regulation of NadK by reduced cofactors.
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