PubMed Health⌕ Search

Biomedical subjects

A Hanaki

Publications and source records attributed to A Hanaki.

At least 19 recordsLinked to original sources
PubMed2000

Autoxidation of ascorbic acid catalyzed by the copper(II) bound to L-histidine oligopeptides, (His)iGly and acetyl-(His)i Gly (i=9, 19, 29). Relationship between catalytic activity and coordination mode.

Spectroscopic and kinetic studies on the autoxidation of ascorbic acid catalyzed by copper complexes of histidine oligopeptides, (His)iGly (i=4, 9, 19, 29), and their acetyl derivatives, Ac-(His)iGly (i=9, 19) have been carried out at pH 4.4 and 25 degrees C under dioxygen. The reaction was monitored at 260 nm using a stopped-flow spectrophotometric technique. The reaction fitted the "Michaelis- Menten" mechanism, and ascorbate was oxidized by the "Ping-Pong" mechanism. The Cu(lI) complexed with the oligopeptide (i > or = 9) enhanced the reaction approximately two-fold relative to the aqueous Cu(II). The catalytic activity depends on the molecular weight which is related to the number of histidyl residues and on the coordination mode of the copper-binding site. Results of circular dichroism (CD) experiments revealed the existence of two types of Cu(II). The catalytically active Cu(II), which is accommodated in the imidazole clusters composed of at least six histidyl residues, exhibits d-d transition bands at 520 and 630 nm, and is easily dissociable, enhances the autoxidation; Ac-(His)19Gly is likely to accommodate approximately three active Cu(II) ions. The Cu(II), which is complexed tightly with the terminal H2N-X-Y-His- moiety, where X and Y denote amino acids, inhibits the autoxidation, and exhibits absorption bands at 480 and 550 nm.

Ascorbic Acid↗
PubMed1996

Glycylsarcosyl-L-histidylglycine, A peptide with a "breakpoint" in complex formation: hydrolysis of the complex [CuH-1L].

Coordination of CU(II) with glycylsarcosyl-L-histidylglycine to form the series of [CuL] and [CuH-1L] was studied potentiometrically and spectroscopically. [CuL] includes the Cu(N2O)O chromophore, in which Cu(II) coordinates with nitrogens from the terminal amino and imidazole groups and a carbonyl oxygen of the Gly-Sar bond, and shows a d-d transition band at 696 nm in the absorption spectrum and at 648 nm in the CD spectrum. The predominant species around pH 8 was [CuH-1L] with Cu(N3O) chromophore, in which Cu(II) coordinates with three nitrogens from a terminal amino, a deprotonated Sar-His peptide bond, and an imidazole of a histidyl residue, and shows the d-d transition band at 652 and 580 nm in the absorption and CD spectra, respectively. This species was hydrolyzed at the Gly-Sar peptide bond, yielding the Cu(II) complex of sarcosyl-L-histidylglycine.

Amino Acid Sequence↗
PubMed1995

Proton nuclear magnetic resonance studies of the complexation of zinc(II) with glycyl-L-histidylglycine.

The complexation of Zn(II) with glycyl-L-histidylglycine and its deuterated derivatives, glycyl-d2-L-histidylglycine and glycyl-L-histidylglycine-d2, was studied by proton nuclear magnetic resonance spectroscopy over the pD range, from 3.4 to 11.0, at 25 degrees C. Addition of Zn(II) to the peptide made the resonances of both imidazole C2-H and C4-H and both methylene-protons of glycyl residues at the amino-terminal and carboxylate end split to three lines in the pD range above 7.0. From the behavior of the C2-H and C4-H chemical shifts, formation of at least two species, in which the imidazole and amino nitrogens coordinated to the metal ion forming a chelate ring, was suggested. Those two species, the ratio of which varied depending on the total concentrations of complexes, seemed to be interconvertible; one referred to as B is a monomer and the other, referred to as C, may be a dimeric or polymeric complex.

Amino Acid Sequence↗
PubMed1994

Synthesis of new oligopeptides and their scavenging abilities against active oxygen species.

The reactivities of new synthetic oligopeptides containing cysteine or histidine towards active oxygen species such as superoxide (O2-) and hydroxyl radical (.OH) were investigated by an electron spin resonance (ESR)-spin trapping method. At physiological pH values, these oligopeptides greatly suppressed the generation of .OH from the reaction of Cu(en)2 (en: ethylenediamine) with hydrogen peroxide (H2O2), although these oligopeptides did not scavenge O2-. The antioxidant mechanism of these oligopeptides is discussed.

Amino Acid Sequence↗
PubMed1993

Copper(II)-albumin complex can activate hydrogen peroxide in the presence of biological reductants: first ESR evidence for the formation of hydroxyl radical.

Copper(II)-albumin complex did not directly react with hydrogen peroxide (H2O2). However, Cu(II)-albumin complex was easily reduced to Cu(I) complex by some biological reductants such as L-cysteine and L-ascorbic acid. Cu(I) complex thus formed could react with H2O2 to give hydroxyl radical (.OH) which was detected by electron spin resonance (ESR) spectroscopy using some water-soluble spin-traps. This result gives the first ESR evidence for the formation of OH radical by the reaction of Cu(II)-albumin with H2O2 in the presence of biological reductants.

Albumins↗
PubMed1992

Reactions of copper(II)-N-polycarboxylate complexes with hydrogen peroxide in the presence of biological reductants: ESR evidence for the formation of hydroxyl radical.

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)

Ascorbic Acid↗
PubMed1991

Evidence for the formation of superoxide ion from the reaction of Cu(II)-ethylenediamine complex with hydrogen peroxide.

Formation of superoxide ion (O2-) from the reaction of CuII(en)2 (en: ethylenediamine) with hydrogen peroxide (H2O2) was first determined spectrophotometrically by use of nitro blue tetrazolium (NBT) in aqueous solutions. From this result, it has been suggested that superoxide ion is generated as an intermediate at the first reaction step between CuII(en)2 and H2O2.

Copper↗
PubMed1991

Copper(II) ethylenediaminetetraacetate complex does activate hydrogen peroxide in the presence of biological reductants.

The reaction of CuII (edta) (edta: ethylenediaminetetraacetic acid) with hydrogen peroxide (H2O2) was studied in the pH range of 6.0 to 8.0. CuII (edta) did not react with H2O2 in the all pH range examined in the absence of biological reductants. CuII (edta), however, could react with H2O2 in the presence of biological reductants such as ascorbic acid, cysteine and NADH to give thibarbituric acid (TBA) reactive substance, regardless of the pH. From these results, it is concluded that CuII (edta) cannot be bound to H2O2 and that the change of the redox potential of Cu2+ ion on ligating with edta may cause CuII (edta) to be unable to oxidize H2O2.

Edetic Acid↗
PubMed1990

Spin-trapping studies on the reactions of Cr(III) with hydrogen peroxide in the presence of biological reductants: is Cr(III) non-toxic?

Cr(III), which is thought to be relatively non-toxic, was reduced to Cr(II) ion by biological reductants such as L-cysteine and NADH and Cr(II) thus formed could easily react with hydrogen peroxide (H2O2) to yield very reactive active oxygen species, hydroxyl radical (.OH). The formation of hydroxyl radical was detected by water-soluble spin-traps, alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN) and 5,5-dimethyl-1-pyrroline N-oxide (DMPO). This result indicates that non-toxic Cr(III) compounds have the possibility of causing dangerous effects to living organism in the presence of biological reductants.

Chromium↗
PubMed1990

ESR spin-trapping studies on the formation of thiosulfate and sulfide radical anions in aqueous solutions.

The first spin-trapping evidence for the formation of thiosulfate (S2O3-.) and sulfide (S-.) radical anions from the reactions of hydrogen peroxide with thiosulphate and sulphide ions, respectively, was presented by electron spin resonance (ESR) spectroscopy using 3,5-dibromo-4-nitrosobenzenesulfonate (DBNBS, 1a) as a spin-trap in aqueous solutions. From the facts that the short-lived radical anions, S2O3-. and S-., could be detected during the oxidation with H2O2, it is suggested that these radical anions may become one of the candidates for the toxicity of sulfide ion in the living body.

Benzenesulfonates↗
PubMed1987

Spin-trapping of sulfite radical anion, SO3-., by a water-soluble, nitroso-aromatic spin-trap.

Sulfite radical anion, SO3-., which is generated either by non-enzymatic reaction of hydrogen peroxide (H2O2-) with sulfite (SO3(2-)) or by the oxidation of bisulfite (HSO3) with Ce4+ ion, can be trapped with a water-soluble, nitroso-aromatic spin-trap, sodium 3,5-dibromo-4-nitrosobenzenesulfonate (DBNBS, 1), yielding an ESR spectrum with coupling constants [aN (1) = 12.9 G, aH (2) = 0.8 G] and a g-value of 2.0063. The SO3- radical adduct (spin adduct) was observed even in the presence of the very low concentration of H2O2 (1.21 X 10(-2) mumol).

Benzenesulfonates↗
PubMed1986

Spin-trapping of superoxide ion by a water-soluble, nitroso-aromatic spin-trap.

Spin-trapping of superoxide ion, O2-, which is produced from two different sources (OH(-)-DMSO and xanthine-xanthine oxidase systems), was investigated by use of a water-soluble, notroso-aromatic spin trap, sodium 3,5-dibromo-4-nitrosobenzene-sulfonate (DBNBS). It was found that O2- from all sources was easily trapped by DBNBS to yield the stable O2- adduct showing the ESR spectrum consisting of a triplet of a triplet [aN (1) = 12.63 G and aH (2) = 0.71 G]. Hydroperoxy radical (HO2.), which can be generated from the oxidation of hydrogen peroxide with Ce4+ ion, was not trapped by DBNBS. These results indicate that the trapped radical is O2-, but not HO2..

Benzenesulfonates↗
PubMed1985

Free radicals of tocopherol model compound, 6-hydroxy-2,2,5,7,8-pentamethylchroman which are produced from the reaction with superoxide ion, O2: studies by high-performance liquid chromatography.

Reaction of superoxide ion, O2-, with alpha-tocopherol model compound, 6-hydroxy-2,2,5,7,8-pentamethylchroman (lb), was investigated by high-performance liquid chromatography (HPLC). Chromatogram of the reaction mixture showed three peaks with retention times of 2.5, 1.8 and 1.5 min, and each peak height was dependent on the concentration of O2. Chemical species having the retention time of 1.5 min was ascribed to chromanoxyl radical (3), and the other chemical species having the retention times of 2.5 and 1.8 min were identified with the model compound (lb) and 2-hydroxy-2-methyl-4-(3, 5, 6-tri-methylbenzoquinone-2-yl) butane (2), respectively. This is a first evidence that the free radicals from tocopherol model compounds was separated by HPLC.

Benzopyrans↗
PubMed1985

Spectroscopic studies on the reaction of superoxide ion with tocopherol model compound, 6-hydroxy-2,2,5,7,8-pentamethylchroman.

The reaction of superoxide ion, O2-, with alpha-tocopherol model compound, 6-hydroxy-2,2,5,7,8-pentamethylchroman (1b), was investigated spectrophotometrically in acetonitirle. The transient absorption (lambda max = 330 nm) observed at the initial stage of the reaction was ascribed to the chromanoxyl-type radical, one-elecron oxidation product of compound 1b, on the basis of the spectroscopic [ultraviolet (UV)/visible and electron spin resonance (ESR)] data. Further, the final product observed was ascribable to the tocopherol quinone (3).

Benzopyrans↗
PubMed1983

Reactions of superoxide ion with tocopherol and its model compounds: correlation between the physiological activities of tocopherols and the concentration of chromanoxyl-type radicals.

Reactions of tocopherol model compounds with superoxide ion (02-) were investigated. 6-Hydroxy-2,2,5,7,8-pentamethylchroman (alpha-model), 6-hydroxy-2,2,5,7-tetramethylchroman and 6-hydroxy-2,2,5,8-tetramethylchroman (beta-model) were oxidized by O2- to yield chromanoxyl radicals which gave ESR spectra, but the radical species were not obtained from 6-hydroxy-2,2,7,8-tetramethylchroman (gamma-model) and 6-hydroxy-2,2-dimethylchroman, both of which do not have a methyl substituent at the C-5 position. ESR studies of the reactions of O2- with tocopherols or their model compounds indicate that the radical concentrations from tocopherol models correlate with the physiological activities of the tocopherols.

Anions↗
PubMed1978

Electron spin resonance studies of radicals obtained by the reaction of alpha-tocopherol and its model compound with superoxide ion.

alpha-Tocopherol (vitamin E) and its model compound, 6-hydroxy-2,2,5,7,8-pentamethylchroman, were found to be oxidized by O2- to yield free radicals which were detected at room temperature by ESR spectroscopy. The ESR spectra of these radicals showed seven main lines with additional hyperfine structure and have the same g-values at 2.0046. Assignments of the ESR spectra were done on the basis of the spectra of the free radicals of deuterated hydroxypentamethylchroman obtained from the same reaction with O2-. The radicals observed are chromanoxyls generated by the abstraction of hydrogen from the 6-hydroxy group of tocopherols.

Electron Spin Resonance Spectroscopy↗