Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:Q8NEX9 (reductase)
 26,410 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Beef heart muscle has been found to contain an enzyme which will rapidly and directly reduce metmyoglobin in vitro. Reduction rates are far greater than any previously reported for nonspecific or nonenzymatic systems. The enzyme is NADH-dependent and requires the presence of ferrocyanide ion for in vitro assay. The artificial electron carriers, dichlorophenolindophenol and methylene blue, are not required. Nonenzymatic reduction of metmyoglobin, which has previously been reported, was not encountered under the assay conditions described herein. Demonstration of enzymatic activity is dependent on a suitable myoglobin substrate, NADH, and ferrocyanide. An equimolar amount of cytochrome b5 was more effective than ferrocyanide in the enzymatic reduction of metmyoglobin. The methods for preparation of beef heart myoglobin and for purification of the enzyme are presented. The enzyme has been purified over 2000-fold. The enzyme has a pH optimum about 6.5 and a Km of 5.0 x 10(-5) M, and is unaffected by the absence of O2. Sodium dodecyl sulfate-gel electrophoresis revealed a molecular weight around 30,000. Purified enzyme does not react with lipoamide. The reaction is markedly influenced by the composition of the buffering milieu. Enzyme activity is inhibited by p-chloromercuriphenyl sulfonic acid, quinacrine dihydrochloride, and N-ethyl-maleimide. Activity was slightly stimulated by FMN. The characteristics of the enzymatic activity and the assay system are similar to those reported by Hegesh et al. (J. Lab. Clin. Med. 72, 339-344, 1968) for erythrocyte methemoglobin reductase.
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PMID:Metmyoglobin reductase. Identification and purification of a reduced nicotinamide adenine dinucleotide-dependent enzyme from bovine heart which reduces metmyoglobin. 44 31

1. Reductive metabolism of p-nitrobenzoic acid and neoprontosil in rat liver microsomes was studied in the presence of haemin, haemoglobin and myoglobin. 2. Microsomal nitro reduction is enhanced 4-fold in the presence of haemoglobin, whereas azo reduction is not affected. 3. Microsomal nitro reduction is enhanced to a similar extent by haemoglobin, haemin and boiled haemoglobin, whereas myoglobin is about half as active. 4. Maximal enhancement of microsomal nitro reductase activity by haemoglobin is achieved at high substrate concentration (6 mM) and low microsomal protein concentration (0.5--1.0 mg/ml). 5. Control microsomal nitro reduction as well as the haemoglobin-enhanced microsomal nitro reduction are inhibited completely by O2 and CO whereas potassium azide as a ligand of ferric haem iron is a less potent inhibitor.
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PMID:Enhancement of nitro reduction in rat liver microsomes by haemin and haemoproteins. 66 50

We report the identification of an NADH-dependent haem-degrading system in ox heart mitochondria. The activity was localized to the mitochondrial inner membrane, specifically associated with complex I (NADH:ubiquinone oxidoreductase). The mitochondrial NADH-dependent haem-degradation activity was highly effective and displayed a rate nearly 60% higher than that of the microsomal activity. The following observations suggested the enzymic nature of the activity: (i) haem degradation by complex I did not proceed upon exposure to elevated temperature and extremes of pH; (ii) it displayed substrate specificity; (iii) it was inhibited by a substrate analogue; and (iv) it showed a cofactor requirement. Moreover, the activity was distinctly different from the ascorbate-mediated haem-degradation activity. Also, complex I differed from the microsomal NADPH:cytochrome c (P-450) reductase inasmuch as the formation of an effective interaction with the microsomal haem oxygenase could not be detected. Addition of purified haem oxygenase to complex I neither influenced the rate of haem degradation nor resulted in the formation of biliverdin IX alpha. In contrast, addition of haem oxygenase to NADPH:cytochrome c (P-450) reductase enhanced the rate of haem degradation by nearly 8-fold, and more than 60% of the degraded haem could be accounted for as biliverdin IX alpha. The haem-degrading activity of complex I appeared to involve the activity of H2O2, as the reaction was inhibited by nearly 90% by catalase, and propentdyopents were detected as reaction products. Intact haemoproteins such as cytochrome c and myoglobin were not effective substrates. However, the haem undecapeptide of cytochrome c was degraded at a rate equal to that observed for haem. Haematohaem was degraded at a rate 50% lower than that observed for haem. It is suggested that the NADH-dependent haem-degradation system may have a biological role in the regulation of the concentration of respiratory haemoproteins and the disposition of the aberrant forms of the mitochondrial haemoproteins.
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PMID:Characterization of an NADH-dependent haem-degrading system in ox heart mitochondria. 312 Jun 97

Recently we reported on the presence of two isoforms of heme oxygenase in rat liver microsomes, referred to as HO-1 and HO-2, and that only HO-1 is inducible (Maines, M. D., Trakshel, G. M., and Kutty, R. K. (1986) J. Biol. Chem. 261, 411-419). Presently we report on the detection of two isoforms of the enzyme in rat testis and purification to near homogeneity of the noninducible isoform, HO-2. A comparative characterization of the liver HO-1 and the testicular HO-2 is also provided. The relative abundance of the isoforms in the two organs was dissimilar. In the testis, the predominant form was HO-2, and only minute amounts of HO-1 were detected. In the liver, however, a 1:2 ratio of HO-1 to HO-2 was noted. The activity of HO-2 in both organs was refractory to cadmium, an inducer of the hepatic HO-1. Under nondenaturing electrophoresis conditions, HO-2 showed a higher mobility than HO-1; on a sodium dodecyl sulfate-polyacrylamide gel, HO-2 displayed a higher monomeric Mr. The apparent Mr values for HO-2 and HO-1 were 36,000 and 30,000, respectively. The isoforms differed in immunochemical properties. Antiserum to the liver HO-1 did not recognize the testicular HO-2 when examined by double immunodiffusion or by Western immunoblotting. HO-2 was more sensitive to heat inactivation than HO-1. When exposed at 65 degrees C (10 min), 70% of HO-1 activity was retained; however, nearly 80% of HO-2 activity was lost. The apparent Km values for heme for HO-1 and HO-2 were 0.24 and 0.40 microM, respectively. HO-1 and HO-2 had similar requirements for cofactor and flavoprotein reductase and were inhibited by heme-ligands (CO, KCN, NaN3). HO-2 utilized as substrate, Fe-protoporphyrin, Fe-hematoporphyrin, and Fe-hematoporphyrin acetate; it did not degrade intact purified rat liver cytochromes b5 and P-450 LM2, catalase, cytochrome c, hemoglobin, or myoglobin.
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PMID:Purification and characterization of the major constitutive form of testicular heme oxygenase. The noninducible isoform. 352 62

Drug oxidations by horseradish peroxidase (HRP), myoglobin (Mb) and cytochrome P-450cam (P-450cam) reconstituted with synthetic hemes were studied in comparison with a form of cytochrome P-450 purified from liver microsomes of polychlorinated biphenyl (PCB)-treated rats. N,N-Dimethylaniline (DMA) and 7-isopropoxycoumarin were hardly dealkylated by the heme-substituted proteins in the presence of NADPH-cytochrome c (P-450) reductase and NADPH, while substantial activity of this kind was observed in the presence of hydrogen peroxide or cumene hydroperoxide as oxygen donors. Specific activity varied, depending on the substrates, oxygen donors, heme derivatives and apoproteins employed. Very high levels of activity were observed in hydrogen peroxide-dependent DMA N-demethylation with HRP substituted with certain hemes. The highest level of activity was about two hundred times as high as that of rat liver cytochrome P-450. The relationship between such activity and the chemical structure of heme derivatives was discussed.
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PMID:Drug oxidation activities of horseradish peroxidase, myoglobin and cytochrome P-450cam reconstituted with synthetic hemes. 368 16

Metmyoglobin (metMb) reduction by metMb reductase from heart muscle requires cytochrome b5 as electron-transfer mediator. The existence of a metMb-ferrous cytochrome b5 complex is demonstrated by mutual perturbation of the proteins' respective electrophoretic titration curves between pH 4 and 7. The same technique shows a preferential binding of cytochrome b5 over metMb by the enzyme. The paramagnetic hyperfine shifts in the cytochrome b5 1H NMR spectrum are perturbed by metMb, indicating the formation of a specific bimolecular complex with a 1:1 stoichiometry and a binding constant estimated to be less than 10 microM. The resonances assigned to the cytochrome b5 heme 6-propionate methylene group exhibit the largest complexation shifts. Computer modeling implicates lysines 47, 50, and 98 of metMb as contact points with cytochrome b5 carboxylate residues 43, 44, 60, and heme 6-propionate. The mechanism of the enzymatic reduction establishes metMb reductase as an NADH-cytochrome b5 oxidoreductase. Cytochrome b5 is reduced at near diffusion-controlled rates by the enzyme with a turnover number of 1000 min-1 X Km for the cytochrome is 0.9 microM versus 100 microM reported for the erythrocyte enzyme. Ferrous cytochrome b5 then reduces metMb nonenzymatically with an apparent rate constant of 4.9 X 10(4) M-1 min-1 X Acetylation of metMb, which does not affect its oxygen affinity or chemical reduction, renders it a poor substrate for enzymatic reduction. This study suggests a function for the three exterior lysine residues conserved in all mammalian myoglobin sequences: they are contact points for complexation with cytochrome b5.
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PMID:Myoglobin: cytochrome b5 interactions and the kinetic mechanism of metmyoglobin reductase. 406 92

Male weanling rats were fed a control diet (46 ppm iron) or an iron-deficient diet (11 ppm iron) for 7 wk to determine the influence of iron deficiency on heme proteins and skeletal muscle mitochondrial respiration. At the end of 7 wk, the hemoglobin in the blood of the iron deficient rats was 35% less and skeletal muscle myoglobin was 20 to 37% less than in the control animals. The concentration of myoglobin in the heart was not appreciably diminished by iron deficiency. Cytochrome c concentration was 20% less in the heart and 35% less in the mixed-fiber gastrocnemius in the iron-deficient animals. Iron deficiency did not influence the activity of metmyoglobin reductase in either heart or skeletal muscle. There was about 30% more methemoglobin reductase activity in the red blood cells of the iron-deficient animals, which resulted in methemoglobin levels that were so low as to be virtually unmeasurable. In the iron-deficient rats, skeletal muscle mitochondrial respiration with either pyruvate-malate or palmitylcarnitine as substrate was 17 to 20% less than in the control animals. This study demonstrates that dietary iron deficiency of sufficient severity to reduce blood Hb and skeletal muscle myoglobin or cytochrome c also results in an impaired skeletal muscle oxidative capacity. The study also illustrates the preferential utilization of iron, not only between tissues, but within tissues, and tissue specific adaptive responses to iron deficiency.
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PMID:Influence of dietary iron deficiency on hemoglobin, myoglobin, their respective reductases, and skeletal muscle mitochondrial respiration. 627 Oct 3

Phenazine methosulfate (PMS) has been successfully used to mediate electron transfer from NADH to cytochrome P-450-CAM in the absence of putidaredoxin and putidaredoxin reductase under aerobic conditions. Identification and quantitation of exo-5- hydroxycamphor , the only product, has been accomplished by gas chromatography. In the absence of cytochrome P-450-CAM, or when other heme proteins (hemoglobin, myoglobin, horseradish peroxidase) are substituted for P-450-CAM, no exo-5- hydroxycamphor is detected. Product formation is not inhibited by the addition of catalase, superoxide dismutase, or hydroxyl radical scavengers; however, significant inhibition is observed with carbon monoxide and metyrapone, known inhibitors of the fully reconstituted P-450 system. Addition of 2,3-dimercaptopropanol to the NADH/PMS/P-450 system leads to a 4-fold increase in product formation; when putidaredoxin is added (without dimercaptopropanol), a 20-fold increase in product formation is observed. Constant bubbling with oxygen results in a further increase in the amount of product (150-fold increase overall). Our results show that PMS can substitute for the electron-transfer proteins putidaredoxin and putidaredoxin reductase in the transfer of electrons from NADH to P-450-CAM, resulting in multiple turnovers. Molecular oxygen dependent multiple turnovers of cytochrome P-450 have not been previously observed without the fully reconstituted, three-protein system.
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PMID:NADH- and oxygen-dependent multiple turnovers of cytochrome P-450-CAM without putidaredoxin and putidaredoxin reductase. 672 35

We found that Toyopearl HW-65C gel matrix adsorbed ferredoxin and ferredoxin-NADP+ reductase in the presence of concentrated ammonium sulfate. Ferredoxin was strongly adsorbed on the gel in 80% saturated ammonium sulfate, and ferredoxin-NADP+ reductase was adsorbed in 40% saturated ammonium sulfate. The phenomenon was utilized for purification of ferredoxin and the reductase on a Toyopearl HW-65C: ammonium sulfate column. The technique greatly simplified the early stage of purification of ferredoxin and the reductase. The improved purification methods further involved column treatments with DEAE-Toyopearl 650M and Matrex Red A. The effectiveness of the columns is reported. Since a number of other proteins such as cytochrome c, myoglobin, chymotrypsinogen A, ovalbumin, and glucose oxidase were also adsorbed well in an appropriately concentrated ammonium sulfate solution, the method may be of general use in enzyme purification.
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PMID:Toyopearl HW-65C: ammonium sulfate as a new column chromatographic adsorbent for enzyme purification. 684 25

A hemoglobin-like protein is found in some of the single-celled organisms, but its structure is quite different from that of mammalian myoglobin or hemoglobin. For instance, a protozoan myoglobin isolated from Paramecium caudatum consists of 116 amino acid residues, so that this contracted form is nearly two thirds of sperm whale myoglobin. Yeast hemoglobin from Candida norvegensis, on the other hand, is composed of a single polypeptide chain with 387 amino acid residues, but of two distinct domains carrying different functions; that is the N-terminal, heme-containing region and the C-terminal, FAD-containing reductase domain. The very unique structures of these ancient hemoproteins tell us their own strategies to overcome many difficulties in the reversible and stable binding of molecular oxygen, a very strong oxidizing agent, to the heme iron(II) in aqueous solutions.
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PMID:The unique structures of protozoan myoglobin and yeast hemoglobin: an evolutionary diversity. 758 95


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