Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: HUMANGGP:001372 (ESR)
 7,313 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The complexation behaviour of Cu(II) with di- and tripeptides containing the aromatic amino acids phenylalanine or typtophan has been investigated at different pH-values and compared with results obtained with di- and triglycine. The results obtained by means of ESR and optical absorption spectroscopy show an influence of the two different aromatic entities on the magnetic and optical parameters. A significant decrease of the g11-value and, concomittantly, an increase of the energy of the d-d transition was measured when an aromatic entity is present in the peptide. A possible explanation for this observation is given.
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PMID:On the influence of aromatic residues on the interaction of copper (II) with small peptides containing aromatic amino acids: ESR and optical studies. 2 Jul 6

Using a combination of ultraviolet-visible absorption, 1H NMR and ESR techniques we have established that N(1) of the imidazole and N(1) of the pyrimidine residues of bleomycin A2 bind to Cu(II) and Zn(II). The observations coupled with the earlier results that the alpha-amino group of the alpha-amino carboxamide function and the carbamoyl moiety are also Cu(II)-ligating groups makes it possible to reconstruct the detailed geometry and stereochemistry of the metal binding site of bleomycin A2.
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PMID:A spectroscopic investigation of the metal binding site of bleomycin A2. The Cu(II) and Zn(II) derivatives. 7 23

High resolution electron spin resonance spectra of the stepwise formation of CN- complexes of Co(II) and Cu(II) carbonic anhydrase show that both metal enzymes form successive 1:1 and 2:1 addition products with CN- at 112 K. The 1:1 complex with the Cu(II) enzyme has a rhombic ESR spectrum similar to the spectra of the 1:1 complexes of the Cu(II) enzyme with CH3COO-, OCN-, N3-, and SH-. The 1:1 complex with the CO(II) enzyme shows a broad resonance at 10 K indicating the presence of high spin Co(II). Previous optical, ESR, and magnetic susceptibility data suggest that the 1:1 complexes are 4-coordinate. At high concentrations of 13CN- the Cu(II) enzyme forms a 2:1 CN- complex with a shift to an axial ESR signal showing ligand nuclear superhyperfine structure from two magnetically equivalent equatorial nitrogen nuclei of the protein and two magnetically equivalent equatorial carbon ligands from two 13CN- anions. Under the same conditions a structurally analogous dicyanide complex of the co(II) enzyme forms with the appearance of and axial ESR signal typical of low spin Co(II). Ligand nuclear superhyperfine structure shows the presence of an axial protein nitrogen as ligand and two magnetically equivalent equatorial carbon ligands from two 13CN- anions. The dicyanide complexes of the Co(II) and Cu(II) enzymes form completely only in frozen solutions and analysis of the ESR spectra show them to have a 5-coordinate square pyrimidal geometry. Comparison of the ligand superhyperfine structure on the ESR signals of both dicyanide complexes shows that there are three nitrogen nuclei of the protein present as ligands at the metal binding site; one axial and two equatorial in the dicyanide complexes. A transient 5-coordinate intermediate might play a role in the mechanism of action of carbonic anhydrase by facilitating ligand exchange reactions within the inner coordination sphere of the Zn(II) ion at the active center.
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PMID:Structure of the active site of carbonic anhydrase as determined by electron spin resonance. 16 45

Previous results indicate that a tryptophan residue(s) may interact with the sugar substrate and Cu(II) atom of galactose oxidase (Ettinger, M. J., and Kosman, D. J. (1974), Biochemistry 13, 1248). We now show that N-bromosuccinimide (NBS) reduces enzymatic activity to 2% as two tryptophans are oxidized; only four residues are easily oxidized in the holoenzyme. An enzymatic activity vs. number of residues oxidized profile suggests that this inactivation is probably associated with only one of the first 2 residues oxidized. There is no evidence for chain cleavage or modification of amino acids other than tryptophan. While substrate protection is not afforded by the sugar substrate, the activity-related tryptophan is placed within the active-site locus by spectral evidence. NBS oxidation of two tryptophans results in a marked diminution of the large copper optical-activity transition at 314 nm. Under some reaction conditions, a doubling of ellipticity in the 600-nm region of copper CD is also observed. The effects of the NBS oxidation on the CD spectra of galactose oxidase permit the assignment of the 314-nm CD band to a charge-transfer transition and the 229-nm extremum to a specific tryptophan contribution. The AZZ parameter from electron spin resonance spectra is also markedly reduced by the NBS oxidation. Moreover, while cyanide binds to the native enzyme without reducing the Cu(II) atom, cyanide rapidly reduces the Cu(II) atom to Cu(I) in the NBS-oxidized enzyme. These CD and ESR results are taken to suggest that one aspect of the inactivation by NBS oxidation may be a conversion of the pseudosquare planar copper complex in the native enzyme to a more distorted, towards tetrahedral, complex in the inactivated enzyme. Since the inactivation can be accomplished without affecting binding of the sugar substrate, tryptophan oxidation must affect catalysis per se.
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PMID:Role of tryptophan in the spectral and catalytic properties of the copper enzyme, galactose oxidase. 19 67

Photosensitivity of dispersion of phosphatidylcholine bilayer liposomes containing purified chlorophyll alpha was examined. The reduction of Cu(II) in the solution outside liposomes was observed upon illumination with visible light under anaerobic condition by means of ESR. The rate of photoreduction was significantly increased by a reductant, potassium ascorbate, localized in the solution of the opposite side of the membrane. The aciton spectrum of the reduction agreed with the absorption spectrum of chlorphyll a in the dispersion. The amount of bleach chlorophyll a was negligible compared with that of reduced (Cu(II). These facts lead to the conclusion that the potoinduced redox reactions at both the membrane-solution interfaces are coupled with each other through the bilayer of each liposome. Kinetic analysis of the reactions based on a possible reaction scheme was carried out and some of the kinetic parameters were determined.
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PMID:Photoinduced charge separation in liposomes containing chlorophyll a. I. Photoreduction of copper(II) by potassium ascorbate through liposome bilayer containing purified chlorophyll a. 22 34

Evidence for the generation of superoxide anion in an enzymatic action of tyrosinase is reported. In the dopatyrosinase reaction, 1 mol of O2 is required for the production of 2 mol of dopaquinone, 1 mol of dopachrome, and 1/4 mol of O2-. Superoxide dismutase and 2-methyl-6-phenyl-3,7-dihydroimidazo[1,2-a]pyrazin-3-one (a chemiluminescence probe and O2 trap) do not inhibit the rate of dopachrome formation from dopa in the presence of tyrosinase, indicating that free O2- is not utilized for metabolizing dopa. ESR studies for the accumulation of semiquinone radicals generated from tyrosine and N-acetyltyrosine in the presence of tyrosinase imply that O2- is not generated by the semiquinone + O2 reaction. Since the addition of H2O2 and dopa to tyrosinase promotes the release of O2- and formation of dopachrome, the Cu(II)O2-Cu(I) complex could be formed as a intermediate (an active form of tyrosinase); [Cu(II)]2 + H2O2 in equilibrium Cu(I)O2-Cu(II) + 2H+.
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PMID:Generation of superoxide during the enzymatic action of tyrosinase. 130 77

The R-state conformation of the Cu(II)-substituted insulin hexamer has been identified, and a number of its derivatives have been studied via 1H NMR, ESR, and UV-visible spectroscopy. This work establishes that the Cu(II)-substituted insulin hexamer undergoes an analogous T to R conformational transition in solution that has been identified previously for Zn(II)- and Co(II)-insulin hexamers [Roy, M., Brader, M.L., Lee, R. W.-K., Kaarsholm, N.C., Hansen, J., & Dunn, M.F. (1989) J. Biol. Chem. 264, 19081-19085]. The data indicate that each Cu(II) center of the R-state Cu(II)-insulin hexamer possesses a coordination site that is accessible to anions from solution. Both phenol and anionic ligands that coordinate to the Cu(II) ions are required to generate the necessary heterotropic interactions that stabilize the R-state structure. With phenylmethylthiolate (PMT), a Cu(II)-R6 adduct that displays the spectral features of blue (type 1) copper proteins is obtained. This complex is proposed to embody a pseudotetrahedral CuIIN3S(PMT) chromophore, in which N is HisB10 (imidazolyl). The remaining ligands examined gave rise to Cu(II)-R6 adducts that possessed the spectral characteristics of normal (type 2) Cu(II) proteins. Under reducing conditions, Cu(I)-T6 and Cu(I)-R6 hexamers have been identified.
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PMID:The T to R transition in the copper(II)-substituted insulin hexamer. Anion complexes of the R-state species exhibiting type 1 and type 2 spectral characteristics. 131 58

The formation of hydroxyl radicals (.OH) by the reaction of CuII(edta) (edta: ethylenediaminetetraacetic acid) with hydrogen peroxide (H2O2) in the presence of biological reductants, such as L-ascorbic acid and L-cysteine, has been demonstrated for the first time by ESR spectroscopy using water-soluble spin-traps, 5,5-dimethyl-1-pyrroline N-oxide (DMPO, 1), alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN, 2) and 3,5-dibromo-4-nitrosobenzenesulfonate (DBNBS, 3). Ethylenediaminetetraacetic acid (edta) is one of the polyamine-N-polycarboxylate chelating agents and it is commonly used by chemists and biochemists. Edta can chelate several metal ions. It is known that the CuII(edta) complex is usually less active than free copper ions in radical reactions, whereas complexes of edta with Fe(II) or Fe(III) still react with hydrogen peroxide (H2O2) or superoxide ion (O2-) (1). In our previous papers (2-4), we also have shown that copper(II) complexes with polyamine-N-polycarboxylates, such as edta and dtpa (diethylenetriaminepentaacetic acid), do not react with H2O2, whereas CuII(en)2 (en: ethylenediamine) can easily do so to give hydroxyl radical (.OH) as a reactive intermediate. Further, we assumed that the change of redox potential of Cu(II) ions as a result of ligation with different ligands causes the difference in reactivity of Cu(II) complexes towards H2O2. To verify this assumption, the reactions of CuII(edta), which was chosen as a Cu(II)-polyamine-N-polycarboxylate complex, with H2O2 were investigated in the presence of some biological reductants, using an ESR-spin trapping method.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Reactions of copper(II)-N-polycarboxylate complexes with hydrogen peroxide in the presence of biological reductants: ESR evidence for the formation of hydroxyl radical. 132 Aug 83

Results are reported of a pH-metric and spectroscopic (CD and ESR) study of the complexes formed between the pseudo-peptide 1-hydroxy-4-(Gly-His-Lys)-anthraquinone (Q-GHK) since, when complexed to copper ions, Q-GHK has been shown to be very effective in promoting the formation of free radicals and inducing DNA cleavage. Q-GHK forms very stable complexes with copper, the major species being bonded to three nitrogen donors in the coordination plane: an imidazole-N of the His residue and the peptide nitrogens of the Gly and His residues. This species is probably stabilized through bonding of the fourth planar coordination site of Cu(II) to the 9-anthraquinone oxygen. At high Q-GHK:copper ratios a second Q-GHK molecule is coordinated through its imidazole-N donor.
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PMID:The coordination of copper(II) to 1-hydroxy-4-(glycyl-histidyl-lysine)-anthraquinone; a synthetic model of anthraquinone anti-cancer drugs. 132 88

Phenylhydrazine cleaved isolated DNA in the presence of Cu(II), Mn(III), hemin, Fe(III)-EDTA, or peroxidase/H2O2, while phenelzine cleaved in the presence of Cu(II). DNA cleavage by phenylhydrazine in the presence of Mn(III), hemin, or Fe(III)-EDTA occurred without marked site specificity. Inhibitory effects of scavengers of hydroxyl free radical (.OH) on the DNA damage suggest the involvement of .OH. On the other hand, Cu(II)-mediated DNA cleavage by phenylhydrazine or phenelzine was inhibited by catalase and bathocuproine, a Cu(I)-specific chelator, but not by .OH scavengers. The predominant cleavage site was the thymine residue of 5'-GTC-3' sequence. Since the cleavage pattern was similar to that induced by Cu(I) plus H2O2 but not to that induced by Cu(II) plus H2O2, it is speculated that the copper-oxygen complex derived from the reaction of H2O2 with Cu(I) participates in DNA damage by phenylhydrazine or phenelzine in the presence of Cu(II). A comparison between scavenger effects on the DNA damage and those on radical production detected with ESR suggests that carbon-centered radicals (phenyl radical, 2-phenylethyl radical) do not play an important role in Cu(II)-, hemin-, or Fe(III)-EDTA-mediated DNA damage by phenylhydrazine or phenelzine of relatively low concentrations (less than 0.5 mM). However, during the oxidation of a high concentration (10 mM) of phenylhydrazine by ferricyanide, phenyl radical seemed to cause DNA damage, especially the breakage of the deoxyribose phosphate backbone. The possibility that active oxygen species (copper-oxygen complex, .OH) are more important in DNA damage induced by hydrazines in vivo than carbon-centered radicals is discussed.
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PMID:Site-specific DNA damage by phenylhydrazine and phenelzine in the presence of Cu(II) ion or Fe(III) complexes: roles of active oxygen species and carbon radicals. 132 22


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