COMPARTMENTATION OF NICOTINAMIDE DINUCLEOTIDE DEHYDROGENASES AND TRANSHYDROGENASES IN NONPHOTOSYNTHETIC PLANT TISSUES

Roles of NAD+ in Acute and Chronic Kidney Diseases

Nicotinamide adenine dinucleotide (oxidized form, NAD⁺) is a critical coenzyme, with functions ranging from redox reactions and energy metabolism in mitochondrial respiration and oxidative phosphorylation to being a central player in multiple cellular signaling pathways, organ resilience, health, and longevity. Many of its cellular functions are executed via serving as a co-substrate for sirtuins (SIRTs), poly (ADP-ribose) polymerases (PARPs), and CD38. Kidney damage and diseases are common in the general population, especially in elderly persons and diabetic patients. While NAD⁺ is reduced in acute kidney injury (AKI) and chronic kidney disease (CKD), mounting evidence indicates that NAD⁺ augmentation is beneficial to AKI, although conflicting results exist for cases of CKD. Here, we review recent progress in the field of NAD⁺, mainly focusing on compromised NAD⁺ levels in AKI and its effect on essential cellular pathways, such as mitochondrial dysfunction, compromised autophagy, and low expression of the aging biomarker αKlotho (Klotho) in the kidney. We also review the compromised NAD⁺ levels in renal fibrosis and senescence cells in the case of CKD. As there is an urgent need for more effective treatments for patients with injured kidneys, further studies on NAD⁺ in relation to AKI/CKD may shed light on novel therapeutics.

NAD(+)/NADH and skeletal muscle mitochondrial adaptations to exercise

The pyridine nucleotides, NAD(+) and NADH, are coenzymes that provide oxidoreductive power for the generation of ATP by mitochondria. In skeletal muscle, exercise perturbs the levels of NAD(+), NADH, and consequently, the NAD(+)/NADH ratio, and initial research in this area focused on the contribution of redox control to ATP production. More recently, numerous signaling pathways that are sensitive to perturbations in NAD(+)(H) have come to the fore, as has an appreciation for the potential importance of compartmentation of NAD(+)(H) metabolism and its subsequent effects on various signaling pathways. These pathways, which include the sirtuin (SIRT) proteins SIRT1 and SIRT3, the poly(ADP-ribose) polymerase (PARP) proteins PARP1 and PARP2, and COOH-terminal binding protein (CtBP), are of particular interest because they potentially link changes in cellular redox state to both immediate, metabolic-related changes and transcriptional adaptations to exercise. In this review, we discuss what is known, and not known, about the contribution of NAD(+)(H) metabolism and these aforementioned proteins to mitochondrial adaptations to acute and chronic endurance exercise.

NAD(+)/NADH and skeletal muscle mitochondrial adaptations to exercise

The pyridine nucleotides, NAD(+) and NADH, are coenzymes that provide oxidoreductive power for the generation of ATP by mitochondria. In skeletal muscle, exercise perturbs the levels of NAD(+), NADH, and consequently, the NAD(+)/NADH ratio, and initial research in this area focused on the contribution of redox control to ATP production. More recently, numerous signaling pathways that are sensitive to perturbations in NAD(+)(H) have come to the fore, as has an appreciation for the potential importance of compartmentation of NAD(+)(H) metabolism and its subsequent effects on various signaling pathways. These pathways, which include the sirtuin (SIRT) proteins SIRT1 and SIRT3, the poly(ADP-ribose) polymerase (PARP) proteins PARP1 and PARP2, and COOH-terminal binding protein (CtBP), are of particular interest because they potentially link changes in cellular redox state to both immediate, metabolic-related changes and transcriptional adaptations to exercise. In this review, we discuss what is known, and not known, about the contribution of NAD(+)(H) metabolism and these aforementioned proteins to mitochondrial adaptations to acute and chronic endurance exercise.

Purification and comparative properties of the cytosolic isocitrate dehydrogenases (NADP) from pea (Pisum sativum) roots and green leaves

The cytosolic isocitrate dehydrogenases (NADP-IDH) were purified to homogeneity from pea roots and green leaves with a high yield by ammonium sulfate precipitation, DEAE-cellulose chromatography, Sephacryl S-200 gel filtration, Matrex red-A affinity chromatography and phenyl-Superose HR 5/5 HPLC. Both isoenzymes were dimeric proteins, consisting of two apparently identical 41-kDa subunits, having similar secondary structures with an alpha-helical content of 20% and a beta-pleated sheet content of 43%. Similarly immunoassays suggested that the two isoenzymes were closely related in terms of antigenic determinants. However, the two proteins were distinguishable by their electrophoretic mobilities and amino acid compositions. The profiles of the two isoenzymes as a function of pH were similar and exhibited a broad pH optimum from 8.5 to 9.0 with Mg2+ as cofactor and 8.0 to 8.5 when Mn2+ was used. Compared to the root isoenzyme, the leaf NADP-IDH appeared to be more heat-labile. However, these isoenzymes exhibited similar behavior for thermal denaturation in the presence of bovine serum albumin and were stabilized upon addition of substrate, metal and coenzyme. Their values of activation energy were estimated as 47 kJ/mol. When using Mn2+ as cofactor, the two isoenzymes displayed identical Km(Mn2+), Km(DL-isocitrate) and Km(NADP) values, which were calculated to be 2.1 microM, 5.7 microM and 2.7 microM respectively. With Mg2+ as cofactor, their Km(Mg2+) K(DL-isocitrate)m and Km(NADP) values were also not statistically different, being 34.0 microM, 15.2 microM and 2.6 microM for the root NADP-IDH, and 29.0 microM, 20.3 microM and 3.1 microM for the leaf isoenzyme. From the above data it can be concluded that although the cytosolic NADP-IDH in pea roots and leaves are organ-specific isozymes, their similar physicochemical and kinetic properties suggest that the two isozymes might be involved in identical metabolic functions.

Soluble electron-transport activities in fresh and aged turnip tissue

A soluble (supernatant) fraction from turnips catalyses the reduction of both FeCN and DCPIP but usually not cytochrome c in the presence of either NADH or NADPH. Slicing and aging turnip tissue induces an increase in these activities as well as the development of an NADH-cytochrome c reductase activity.(NH4)2SO4 and Sephadex fractionation indicated that at least three enzymes were involved: an NADH-cytochrome-c reductase, an NADH-FeCN reductase, and an NAD(P)H-DCPIP and FeCN reductase. While the latter reductase had an acid pH optimum, indicating vacuolar origin, the NADH-cytochrome-c and FeCN reductases both had neutral pH optima, indicating cytoplasmic origin. Characterization of the NADH-specific reductases indicated that NADH-FeCN reductase may be a soluble form of the microsomal membrane NADH dehydrogenase but that NADH-cytochrome-c reductase may be normally soluble and possibly involved in cyanide-sensitive NADH oxidation.The induced development of all three reductases was inhibited by 6-methylpurine, ethionine and cycloheximide, indicating dependence on both RNA and protein synthesis. The inhibition by cycloheximide could be reversed but this reversion required a 20-h washing-out period to be complete.

Comparative aspects of some bacterial dehydrogenases and transhydrogenases

Ragland, T. E. (Brandeis University, Waltham, Mass.), T. Kawasaki, and J. M. Lowenstein. Comparative aspects of some bacterial dehydrogenases and transhydrogenases. J. Bacteriol. 91:236-244. 1966.-Twenty-eight diverse bacterial species were surveyed for the activities and coenzyme specificities of four enzymes: isocitrate dehydrogenase (ICDH), glucose-6-phosphate dehydrogenase (G-6-PDH), 6-phosphogluconate dehydrogenase (6-PGDH), and reduced nicotinamide adenine dinucleotide phosphate-nicotinamide adenine dinucleotide (NAD) transhydrogenase (TH). Most of the species that exhibited a nicotinamide adenine dinucleotide phosphate (NADP)-linked ICDH also showed significant TH activity, but there were several which did not. Only one of the organisms tested, Xanthomonas pruni, had an ICDH active with both NAD and NADP; it was devoid of TH activity. Acetobacter suboxydans, which lacks ICDH altogether, also had no TH. Some of the species examined had G-6-PDH or 6-PGDH (or both) of dual coenzyme specificity, but there was no apparent relation between these findings and the presence or absence of TH. The TH reaction was assayed by use of analogues of NAD as acceptors. The bacteria could be divided into two groups on the basis of TH specificity, one group reacting at a much faster rate with the 3-acetylpyridine analogue of NAD than with the thionicotinamide analogue, whereas the converse was true for the other group. A few organisms showed no marked specificity for either analogue. This division of specificity can be related to the currently accepted taxonomic classification of the organisms, although a few apparent anomalies were found.