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PubMed1982

Changes in the composition and fluidity of membranes in obese (ob/ob) mice: a study of hepatic microsomal NADPH-cytochrome P450 oxidoreductase activity.

The characteristics of microsomal membrane lipids in obese (ob/ob) mice have been probed by studies on the microsomal enzyme NADPH-cytochrome P450 oxidoreductase and by investigation of their fluidity using the fluorescence probe 1,6 diphenylhexatriene. Arrhenius plots of NADPH-cytochrome P450 oxidoreductase activity were biphasic with the break temperature in obese mice reduced from 9.5 to 6.5 degrees C. The activation energy of NADPH-cytochrome P450 oxidoreductase was increased in obese microsomes below the Arrhenius breakpoint. Normalising the body temperature of ob/ob mice did not rectify the Arrhenius plot of NADPH-cytochrome P450 oxidoreductase activity of ob/ob mice. DPH fluorescence polarisation indicated that the gross phospholipids from ob/ob mouse microsomes were more fluid than those from lean mice. Phosphatidylethanolamine (PE) of ob/ob microsomes contains a higher proportion of unsaturated fatty acids resulting mainly from an increase in 22:6 and a fall in 16:0. Phosphatidyl choline (PC) of ob/ob microsomes contains an increased proportion of saturated fatty acids. Phospholipid vesicles of obese microsomal PE were more fluid and obese microsomal PC less fluid than the equivalent phospholipids from lean mice microsomes. The changes in Arrhenius plots of NADPH-cytochrome P450 oxidoreductase activity of obese microsomes are interpreted in relation to the reported phospholipid changes.

Animals↗
PubMed1994

Xanthine oxidoreductase release after descending thoracic aorta occlusion and reperfusion in rabbits.

Cardiopulmonary and other organ dysfunction often occurs after operation on the descending thoracic aorta. Though there are multiple causes of organ dysfunction in this setting, free radical injury may play a prominent role. Xanthine oxidoreductase, an enzyme that generates oxidants after exposure to ischemia, could be released from ischemic liver and intestine during reperfusion. To test this hypothesis, we created aortic occlusion in eight rabbits for 40 minutes by inflation of a 4F Fogarty balloon catheter in the descending thoracic aorta. Eight sham-operated rabbits served as a control group. Two hours of reperfusion followed removal of the balloon catheter. Hemodynamic and acid-base status were maintained near baseline values during reperfusion. Plasma samples were obtained for determination of the activity of the hepatocellular enzymes xanthine oxidoreductase, aspartate aminotransferase, alanine transferase, and lactate dehydrogenase. Plasma xanthine oxidoreductase activity increased significantly (p < 0.001) during reperfusion (729 +/- 140 microU/ml, mean +/- standard error of the mean) compared with baseline (132 +/- 18 microM/mL). The other enzymes followed a similar pattern of release. We report the release of xanthine oxidoreductase in an animal model that simulates the situation of human thoracic aorta operations. The oxidants produced by the circulating xanthine oxidoreductase observed during reperfusion would likely be toxic to vascular endothelium, potentially contributing to multiple organ dysfunction.

Alanine Transaminase↗
PubMed1993

Quinoline oxidoreductase from Pseudomonas putida 86: an improved purification procedure and electron paramagnetic resonance spectroscopy.

Quinoline oxidoreductase, an iron-sulfur molybdenum flavoprotein containing flavin adenine dinucleotide and molybdopterin cytosine dinucleotide, was purified from Pseudomonas putida 86 to homogeneity. The various electron-transfer centers of the purified enzyme were examined by electron paramagnetic resonance spectroscopy. Quinoline deuterated at position 2 was prepared by deuterodecarboxylation of 2-quinolinecarboxylic acid. Quinoline added to the enzyme elicited the Mo(V) "rapid" type Q signal arising from the complex of enzyme and substrate, whereas in oxidized quinoline oxidoreductase a Mo(V) "resting" signal was observed. EPR spectroscopy at helium temperatures below 70 K revealed the existence of two types of iron-sulfur centers, Fe-S I and Fe-S II. An organic free radical appeared upon reduction with sodium dithionite. Inactivation of the enzyme by cyanide led to the inactive desulfo quinoline oxidoreductase, which yielded another Mo(V) signal designated "slow" type Q upon reduction with dithionite. Desulfo quinoline oxidoreductase was partially reactivated by incubation with sulfide.

Cyanides↗
PubMed1981

Intrinsic dichlorophenolindophenol reductase activity associated with the superoxide-generating oxidoreductase of human granulocytes.

NADPH-dependent dichlorophenolindophenol (DCIP) reductase activity cosediments with NADPH-dependent O(2-)-generating activity in subcellular particulate fractions of zymosan-stimulated human polymorphonuclear leukocytes (PMN's). Subcellular fractions derived from unstimulated PMN's were devoid of both activities, as were fractions from zymosan-stimulated PMN's of a patient known to have chronic granulomatous disease. NADPH-dependent DCIP reduction associated with the oxidoreductase-rich subcellular fractions was unaffected by addition of excess superoxide dismutase sufficient to abolish all traces of O2- production as measured by conversion of ferricytochrome c to its ferrous form. Moreover, DCIP inhibited NADPH-dependent production of O2- in subcellular fractions derived from normal donors. In contrast to the subcellular studies, whole cell suspensions were ineffective in reducing extracellular DCIP despite their capacity to generate O2-, albeit at a lesser rate, in the presence of this electron-accepting dye. These results demonstrate that DCIP reductase activity is associated with the oxidoreductase complex and suggest that it is located on the inner side of the PMN's plasma membrane. The stability of the oxidoreductase complex is markedly improved by storage in glycerol. Both overall O(2-)-generating activity and DCIP reductase activity exhibit a similar pH optimum of 7.0. The Km of the oxidoreductase complex for DCIP is 33 micro M.

Granulocytes↗
PubMed1997

Pyruvate ferredoxin oxidoreductase from the hyperthermophilic archaeon, Pyrococcus furiosus, functions as a CoA-dependent pyruvate decarboxylase.

Pyruvate ferredoxin oxidoreductase (POR) has been previously purified from the hyperthermophilic archaeon, Pyrococcus furiosus, an organism that grows optimally at 100 degrees C by fermenting carbohydrates and peptides. The enzyme contains thiamine pyrophosphate and catalyzes the oxidative decarboxylation of pyruvate to acetyl-CoA and CO2 and reduces P. furiosus ferredoxin. Here we show that this enzyme also catalyzes the formation of acetaldehyde from pyruvate in a CoA-dependent reaction. Desulfocoenzyme A substituted for CoA showing that the cofactor plays a structural rather than a catalytic role. Ferredoxin was not necessary for the pyruvate decarboxylase activity of POR, nor did it inhibit acetaldehyde production. The apparent Km values for CoA and pyruvate were 0.11 mM and 1.1 mM, respectively, and the optimal temperature for acetaldehyde formation was above 90 degrees C. These data are comparable to those previously determined for the pyruvate oxidation reaction of POR. At 80 degrees C (pH 8.0), the apparent Vm value for pyruvate decarboxylation was about 40% of the apparent Vm value for pyruvate oxidation rate (using P. furiosus ferredoxin as the electron acceptor). Tentative catalytic mechanisms for these two reactions are presented. In addition to POR, three other 2-keto acid ferredoxin oxidoreductases are involved in peptide fermentation by hyperthermophilic archaea. It is proposed that the various aldehydes produced by these oxidoreductases in vivo are used by two aldehyde-utilizing enzymes, alcohol dehydrogenase and aldehyde ferredoxin oxidoreductase, the physiological roles of which were previously unknown.

Aldehyde Oxidoreductases↗
PubMed1983

Methylenetetrahydrofolate reductase. Steady state and rapid reaction studies on the NADPH-methylenetetrahydrofolate, NADPH-menadione, and methyltetrahydrofolate-menadione oxidoreductase activities of the enzyme.

Methylenetetrahydrofolate reductase is a flavoprotein which has recently been purified to homogeneity from pig liver (Daubner, S. C., and Matthews, R. G. (1982) J. Biol. Chem. 257, 140-145). The enzyme catalyzes the transfer of reducing equivalents from NADPH to menadione or methylenetetrahydrofolate, or from methyltetrahydrofolate to menadione. We have now examined the individual reductive and oxidative half-reactions comprising these activities, measuring the rate of flavin reduction or oxidation in an anaerobic stopped flow apparatus. In all cases, the individual half-reactions occur at rates which are sufficiently fast to account for catalytic turnover, indicating that the enzyme is kinetically competent to catalyze these oxidoreductions by Ping Pong Bi Bi mechanisms. NADPH-linked reduction of the flavin appears to be rate-limiting for the NADPH-menadione oxidoreductase reaction, while reoxidation of the flavin is partially rate-limiting in the NADPH-methylenetetrahydrofolate oxidoreductase reaction. Reduction of the flavin by methyltetrahydrofolate is rate-limiting in the methyltetrahydrofolate-menadione oxidoreductase reaction. No intermediates are seen in any of these half-reactions. In agreement with our postulate of ping-pong mechanisms for the catalytic reactions of the enzyme is our observation of exchange of radiolabel between [methyl-14C]methyltetrahydrofolate and [methylene-14C]methylenetetrahydrofolate in the absence of either menadione or pyridine nucleotides. The rate of exchange when both substrates are saturating is in good agreement with the rate of the methyltetrahydrofolate-menadione oxidoreductase reaction measured under Vmax conditions.

5,10-Methylenetetrahydrofolate Reductase (FADH2)↗
PubMed1997

Unusual conformation of nicotinamide adenine dinucleotide (NAD) bound to diphtheria toxin: a comparison with NAD bound to the oxidoreductase enzymes.

The conformation of NAD bound to diphtheria toxin (DT), an ADP-ribosylating enzyme, has been compared to the conformations of NAD(P) bound to 23 distinct NAD(P)-binding oxidoreductase enzymes, whose structures are available in the Brookhaven Protein Data Bank. For the oxidoreductase enzymes, NAD(P) functions as a cofactor in electron transfer, whereas for DT, NAD is a labile substrate in which the N-glycosidic bond between the nicotinamide ring and the N-ribose is cleaved. All NAD(P) conformations were compared by (1) visual inspection of superimposed molecules, (2) RMSD of atomic positions, (3) principal component analysis, and (4) analysis of torsion angles and other conformational parameters. Whereas the majority of oxidoreductase-bound NAD(P) conformations are found to be similar, the conformation of NAD bound to DT is found to be unusual. Distinctive features of the conformation of NAD bound to DT that may be relevant to DT's function as an ADP-ribosylating enzyme include (1) an unusually short distance between the PN and N1N atoms, reflecting a highly folded conformation for the nicotinamide mononucleotide (NMN) portion of NAD, and (2) a torsion angle chi N approximately 0 degree about the scissile N-glycosidic bond, placing the nicotinamide ring outside of the preferred anti and syn orientations. In NAD bound to DT, the highly folded NMN conformation and torsion angle chi N approximately 0 degree could contribute to catalysis, possibly by orienting the C1'N atom of NAD for nucleophilic attack, or by placing strain on the N-glycosidic bond, which is cleaved by DT. The unusual overall conformation of NAD bound to DT is likely to reflect the structure of DT, which is unusual among NAD(P)-binding enzymes. In DT, the NAD binding site is formed at the junction of two antiparallel beta-sheets. In contrast, although the 24 oxidoreductase enzymes belong to at least six different structural classes, almost all of them bind NAD(P) at the C-terminal end of a parallel beta-sheet. The structural alignments and principal component analysis show that enzymes of the same structural class bind to particularly similar conformations of NAD(P), with few exceptions. The conformation of NAD bound to DT superimposes closely with that of an NAD analogue bound to Pseudomonas exotoxin A, an ADP-ribosylating toxin that is structurally homologous to DT. This suggests that all of the ADP-ribosylating enzymes that are structurally homologous to DT and ETA will bind a highly similar conformation of NAD.

Catalase↗
PubMed1995

Pyruvate: ferredoxin oxidoreductase from the sulfate-reducing Archaeoglobus fulgidus: molecular composition, catalytic properties, and sequence alignments.

Archaeoglobus fulgidus is a hyperthermophilic sulfate-reducing archaeon. In this communication we describe the purification and properties of pyruvate: ferredoxin oxidoreductase from this organism. The catabolic enzyme was purified 250-fold to apparent homogeneity with a yield of 16%. The native enzyme had an apparent molecular mass of 120 kDa and was composed of four different subunits of apparent molecular masses of 45, 33, 25, and 13 kDa, indicating an alpha beta gamma delta structure. Per mol, the enzyme contained 0.8 mol thiamine pyrophosphate, 9 mol non-heme iron, and 8 mol acid-labile sulfur. FAD, FMN, lipoic acid, and copper were not found. The purified enzyme showed an apparent Km for coenzyme A of 0.02 mM, for pyruvate of 0.3 mM, and for clostridial ferredoxin of 0.01 mM, an apparent Vmax of 64 U/mg (at 65 degrees C) with a pH optimum near 7.5 and an Arrhenius activation energy of 75 kJ/mol (between 30 and 70 degrees C). The temperature optimum was above 90 degrees C. At 90 degrees C, the enzyme lost 50% activity within 60 min in the presence of 2 M KCl. The enzyme did not catalyze the oxidation of 2-oxoglutarate, indolepyruvate, phenylpyruvate, glyoxylate, and hydroxypyruvate. The N-terminal amino acid sequences of the four subunits were determined. The sequence of the alpha-subunit had similarities to the N-terminal amino acid sequence of the alpha-subunit of the heterotetrameric pyruvate: ferredoxin oxidoreductase from Pyrococcus furiosus and from Thermotoga maritima, and unexpectedly, to the N-terminal amino acid sequence of the homodimeric pyruvate:ferredoxin oxidoreductase from proteobacteria and from cyanobacteria. No sequence similarities were found, however, between the alpha-subunits of the enzyme from A. fulgidus and the heterodimeric pyruvate:ferredoxin oxidoreductase from Halobacterium halobium.

Amino Acid Sequence↗
PubMed1989

Purification and characterization of the pyruvate-ferredoxin oxidoreductase from Clostridium acetobutylicum.

The pyruvate-ferredoxin oxidoreductase from Clostridium acetobutylicum was purified to homogeneity and partially characterized. A 9.2-fold purification was achieved in a three step purification procedure: ammonium sulfate fractionation, chromatography on Phenyl Sepharose and on Procion Blue H-EGN12. The pure enzyme exhibited a specific activity of 25 U/mg of protein. Homogeneity of the pyruvate-ferredoxin oxidoreductase was confirmed by native polyacrylamide gel electrophoresis and sodium dodecylsulfate (SDS)-polyacrylamide gel electrophoresis. The molecular weight was determined to be 123,000/monomer. The subunit composition of the native enzyme could not be determined because of the instability of the pure enzyme. The pyruvate-ferredoxin oxidoreductase is sensitive to oxygen and dilution during purification. The dilution inactivation could be partially overcome by the addition of 300 microM coenzyme A or 50% ethyleneglycol. A thiamine pyrophosphate content of 0.39 mol per mol of enzyme monomer was found, the iron and sulfur content was 4.23 and 0.91, respectively. The pH-optimum was at pH 7.5 and the temperature optimum was at 60 degrees C. Kinetic constants were measured in the forward reaction. The apparent Km for pyruvate and coenzyme A were 322 microM and 3.7 microM, respectively. With 2-ketobutyrate the pyruvate-ferredoxin oxidoreductase showed 12.5% of the activity compared to pyruvate. No activity was found with 2-ketoglutarate. Ferredoxin from Clostridium pasteurianum could be used as physiological electron acceptor.

Chromatography, Ion Exchange↗
PubMed1983

Identification of thiol:protein disulfide oxidoreductase activity in cultured human fibroblasts: dependence of enzyme activity on growth conditions.

Thiol:protein disulfide oxidoreductase activity was assayed in extracts of cultured normal human skin fibroblasts. Enzyme activity in confluent fibroblasts was dependent on growth conditions. In serum-deprived fibroblasts grown in minimal medium enzyme activity was approximately 40% of that observed in fibroblasts maintained in medium supplemented with 10% fetal calf serum. In fibroblasts cultured in medium supplemented only with insulin, activity was 35% greater than that in fibroblasts cultured in unsupplemented defined medium. Antibodies raised against purified bovine liver thiol:protein disulfide oxidoreductase immunoprecipitated all of the activity present in fibroblast extracts. The thiol:protein disulfide oxidoreductase from human fibroblasts thus appears to share antigenic determinants with the bovine liver enzyme. The human fibroblast may serve as an in vitro model to study the regulation of the oxidoreductase.

Blood↗
PubMed1992

The influence of lipid peroxidation products (malondialdehyde, 4-hydroxynonenal) on xanthine oxidoreductase prepared from rat liver.

Depending on metabolic conditions, xanthine oxidoreductase acts as either a dehydrogenase (XDH) or an oxidase (XOD). The metabolism of hypoxanthine and xanthine by the oxidase is associated with the production of reactive oxygen radicals. Reaction of reactive oxygen radicals with polyunsaturated fatty acids (lipid peroxidation) leads to the formation of malondialdehyde (MDA) and 4-hydroxynonenal (HNE), known to modify proteins by reaction with NH2- and SH-groups. Therefore, these aldehydes could influence both the activity of xanthine oxidoreductase and the XOD/XDH ratio. We found that incubation of xanthine oxidoreductase with MDA leads to an initial increase in XDH activity and to a continuous decrease in XOD activity, whereby the total activity decreases. This was in contrast to the effects of HNE which did not alter the XDH activity; XOD was however activated. This demonstrates that the lipid peroxidation products MDA and HNE are able to modify xanthine oxidoreductase similarly to a feed-back mechanism.

Aldehydes↗
PubMed1995

HOQNO interaction with cytochrome b in succinate:menaquinone oxidoreductase from Bacillus subtilis.

2-n-Heptyl 4-hydroxyquinoline-N-oxide (HOQNO) inhibits the succinate:quinone oxidoreductase activity of isolated and membrane-bound succinate:menaquinone oxidoreductase of B. subtilis. The inhibition pattern resembles closely that observed for alpha-thenoyltrifluoroacetone and carboxins in the mitochondrial succinate:ubiquinone oxidoreductase: ca. 90% of the activity is highly sensitive to HOQNO (Ki ca. 0.2 microM for the isolated enzyme) whereas the rest 10% proves to be resistant to the inhibitor. HOQNO binding is shown to perturb the absorption spectrum of the ferrous di-heme cytochrome b of the B. subtilis succinate:quinone oxidoreductase both in the alpha and Soret bands. In addition, the inhibitor is shown to bring about a negative shift of Em of the low-potential heme b. It is suggested that HOQNO interacts with a menasemiquinone binding site near the low-potential heme and suppresses the MQ.(-)-to-MQH2 step of the quinone reductase reaction but allows partly for the MQ-to-MQ.- transition to occur; dismutation of MQ. formed in the latter reaction to MQ and MQH2 may account for the 10% of the enzyme activity insensitive to HOQNO.

Bacillus subtilis↗
PubMed1989

Xanthine:acceptor oxidoreductase activities in ischemic rat skin flaps.

Xanthine:acceptor oxidoreductase activities were assayed in free skin flaps following prolonged preservation. In normal rat skin, xanthine dehydrogenase transfers electrons to NAD+ and accounts for 73% of total oxidoreductase activity, and xanthine oxidase transfers electrons to molecular oxygen and accounts for the remaining 27%. Xanthine oxidase activity increased significantly in skin flaps during ischemia: approximately 30 and 100% increases after 6 and 24 hr of ischemia, respectively. Allopurinol inhibited xanthine oxidoreductase activity: free skin flaps obtained from allopurinol-treated animals exhibited a low level of xanthine oxidoreductase activity throughout the period of preservation. Systemic allopurinol significantly improved the survival rate from 32 to 75% of free flaps transferred after 24 hr of preservation at room temperature. These observations suggest that the xanthine oxidase system is a major source of oxygen free radicals following ischemia/reperfusion in skin. The increase in xanthine oxidase is attributable to the conversion of xanthine dehydrogenase to oxidase, a conversion which involves sulfhydryl oxidation in skin flaps.

Allopurinol↗
PubMed1985

Purification and resolution of NADH diaphorase activity from NADPH diaphorase-linked: O2 oxidoreductase activity of human neutrophils.

Intrinsic NADPH diaphorase activity is a component of the membrane-bound NAD(P)H:O2 oxidoreductase of human neutrophils. NADH-specific diaphorase activity is also present in membrane fractions rich in oxidoreductase activity. Studies were undertaken to determine whether the NADH diaphorase might also be intrinsic to the oxidoreductase. The latter diaphorase was freed from the membrane by detergent extraction and partially purified approximately 80-fold. Its apparent molecular weight following solubilization in deoxycholate and Tween-20 was 204 000 +/- 10 000. The specific activity of the partially purified diaphorase with ferricyanide as electron acceptor was 7.6 X 10(3) mU/mg protein, its pH optimum was 7.0, and its Km for NADH was 13 microM. It is completely devoid of NADPH diaphorase activity, lacks the capacity to reduce molecular oxygen, yet readily reduces ferricyanide, 2,6-dichlorophenolindophenol and ferricytochrome c. Whereas the NADH diaphorase was freed from the particulate fraction of cell lysates by extraction in 10 mM Tris-HCl buffer (pH 8.6) made up in 15% glycerol and 0.5% Tween-20, NADPH-dependent diaphorase and superoxide-generating activities also present in the membrane were not. These observations make it unlikely that the principal membrane-bound NADH diaphorase found in human neutrophils is a component of the NAD(P)H:O2 oxidoreductase, despite its common association in the same particulate fraction of cell lysates.

Chromatography, Gel↗
PubMed1988

The 47-kDa protein involved in the NADPH:O2 oxidoreductase activity of human neutrophils is phosphorylated by cyclic AMP-dependent protein kinase without induction of a respiratory burst.

When human neutrophilic granulocytes are stimulated with chemoattractants or phorbol esters, these cells respond with a so-called respiratory burst: such stimuli induce the activation of a NADPH:O2 oxidoreductase, which converts oxygen into superoxide. This activation coincides with the phosphorylation of a number of proteins, amongst which a 47-kDa phosphoprotein. Neutrophils from patients with the autosomal form of chronic granulomatous disease (CGD) fail to mount a respiratory burst and concomitantly lack phosphorylation of the 47-kDa protein. We have shown this protein to be a substrate for protein kinase C. In the present paper we describe the phosphorylation of the 47-kDa phosphoprotein by cyclic AMP-dependent protein kinase. For these studies, we used neutrophil cytoplasts, i.e., neutrophils devoid of nucleus and granules, but with an intact NADPH:O2 oxidoreductase. Addition of dibutyryl cyclic AMP (Bt2cAMP) to intact human neutrophil cytoplasts resulted in an increase in protein phosphorylation. Among the phosphorylated proteins is a 47-kDa phosphoprotein. Increased protein phosphorylation was also observed upon addition of Bt2cAMP to neutrophil cytoplast lysates. In lysates of neutrophil cytoplasts from patients with the autosomal form of CGD, phosphorylation of the 47-kDa protein was absent. This finding (confirmed by analysis on two-dimensional gels) indicates that the 47-kDa phosphoprotein, relevant for the NADPH:O2 oxidoreductase, is a substrate for the cAMP-dependent protein kinase. Unlike phorbol ester-induced phosphorylation, Bt2cAMP-induced phosphorylation is not accompanied by initiation of a respiratory burst. This observation demonstrates that 47-kDa phosphoprotein phosphorylation can be uncoupled from respiratory burst activity and indicates that other modifications of the NADPH:O2 oxidoreductase are required for induction of activity.

Bucladesine↗
PubMed1976

Regulation of the NADH and NADPH-ferredoxin oxidoreductases in clostridia of the butyric group.

NADH and NADPH-ferredoxin oxidoreductases have been studied in Clostridium acetobutylicum, Cl. tyrobutyricum and Cl. pasteurianum. The study of the distribution and regulation of these enzymatic activities in well-defined culture conditions, reveals that the essential function of NADPH-ferredoxin oxidoreductase is to produce NADPH, while NADH-ferredoxin oxidoreductase can, depending on cellular conditions, produce or oxidize NADH. When these Clostridia use glycolysis, regulation of the NADH-ferredoxin oxidoreductase by acetyl-CoA (obligatory activator of NADH-ferroxin reductase activity) and by NADH (competitive inhibitor of ferredoxin-NAD+ reductase activity) allow the enzymes to function correlatively with glyceraldehyde-3-phosphate dehydrogenase and thus control the levels of NAD+ and NADH in the cell. In Cl. tyrobutyricum and Cl. pasteurianum, the ferredoxin-NADP+ reductase activities are regulated by NAD+ and NADH in accordance with the intracellular concentrations of these coenzymes. In Cl. tyrobutyricum growing on pyruvate/acetate, NADH and NADPH-ferredoxin reductase activities cannot be detected; only the ferredoxin-NAD+ and ferredoxin-NADP+ reductase activities are found. In this Clostridium, regulation of the ferredoxin-NADP+ reductase activity is the same whether it is grown on glucose or pyruvate. Contrary to this, the ferredoxin-NAD+ reductase activity undergoes a drastic change, since NADH no longer controls the enzymatic activity. In this case regulation is no longer necessary, since glyceraldehyde-3-phosphate dehydrogenase does not function.

Butyrates↗
PubMed1989

Comparison of xanthine: NAD+ oxidoreductase from liver of toad Bufo viridis and other vertebrates.

1. Xanthine oxidoreductase was isolated from toad Bufo viridis (a mainly ureotelic amphibian species) and partially purified. The enzyme occurred as a stable xanthine: NAD+ oxidoreductase (EC 1.1.1.204), unconvertible to the oxidase form. 2. Some properties of the enzyme resembled those of xanthine oxidoreductase from an ammonotelic fish, Cyprinus carpio, and the ureotelic rat, but in other aspects it was similar to this enzyme from an uricotelic snake, Natrix natrix. 3. Inhibition of the toad enzyme by NADH at high non-physiological concentrations rules out a modulation of its oxypurine-hydroxylating activity by in vivo changes in the NADH/NAD+ ratio. Therefore, toad xanthine oxidoreductase plays no regulatory role in the purine nucleotide metabolism.

Animals↗
PubMed2001

Na(+) translocation by bacterial NADH:quinone oxidoreductases: an extension to the complex-I family of primary redox pumps.

The current knowledge on the Na(+)-translocating NADH:ubiquinone oxidoreductase of the Na(+)-NQR type from Vibrio alginolyticus, and on Na(+) transport by the electrogenic NADH:Q oxidoreductases from Escherichia coli and Klebsiella pneumoniae (complex I, or NDH-I) is summarized. A general mode of redox-linked Na(+) transport by NADH:Q oxidoreductases is proposed that is based on the electrostatic attraction of a positively charged Na(+) towards a negatively charged, enzyme-bound ubisemiquinone anion in a medium of low dielectricity. A structural model of the [2Fe-2S]- and FAD-carrying NqrF subunit of the Na(+)-NQR from V. alginolyticus based on ferredoxin and ferredoxin:NADP(+) oxidoreductase suggests that a direct participation of the Fe/S center in Na(+) transport is rather unlikely. A ubisemiquinone-dependent mechanism of Na(+) translocation is proposed that results in the transport of two Na(+) ions per two electrons transferred. Whereas this stoichiometry of the pump is in accordance with in vivo determinations of Na(+) transport by the respiratory chain of V. alginolyticus, higher (Na(+) or H(+)) transport stoichiometries are expected for complex I, suggesting the presence of a second coupling site.

Amino Acid Sequence↗