Miyako Miki

Osaka University, Suika, Ōsaka, Japan

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Publications (12)37.66 Total impact

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    ABSTRACT: The dependence of the kinetic dynamics of the polystyrene dimer radical cation (Ph2+) on the CCl4 concentration was investigated in a cyclohexane solution by nanosecond pulse radiolysis. A slow formation of (Ph2+) (k=1.5×109M−1s−1) through electron transfer quenching of the polystyrene excimer was observed upon the addition of 10–100mM CCl4. This electron transfer quenching led to an increase of the free ion yield (∼20%).
    No preview · Article · Aug 2006 · Chemical Physics Letters
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    ABSTRACT: Protection effects by aromatic compounds in irradiated liquid n-dodecane were studied as a model experiment for the radiolysis of aliphatic polymers. Final products of γ-radiolysis were analyzed by gas chromatography, while reactivity of additives towards reactive intermediate species was analyzed by pulse radiolysis. The yield of scission products was well reduced by increase of the degree of aromaticity and concentration of additives; moreover, the higher the degree of aromaticity of additive, the higher was the reactivity of additive towards excited molecules, radical cations, and electrons. In conclusion, reactivity between additive and reactive intermediate species is an important factor of radiation protection.
    No preview · Article · Jul 2001 · Radiation Physics and Chemistry
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    ABSTRACT: The highest time resolution of the pulse radiolysis had remained about 30 ps since the late 1960s. To make clear the primary processes in the radiation chemistry and physics within 30 ps, we developed a stroboscopic pulse radiolysis system for the absorption spectroscopy with the time resolution of 2.0 ps (10–90% rise time). The time resolution of 2.0 ps was estimated from the time-dependent behavior of the hydrated electrons. The system consists of a subpicosecond electron linac as an irradiation source, a femtosecond laser as an analyzing light and a jitter compensation system.
    Full-text · Article · Jan 2000 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
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    ABSTRACT: The reduction of flavin in NADH--adrenodoxin reductase by the hydrated electron (eaq-) was investigated by pulse radiolysis. The eaq- reduced directly the flavin of the reductase to form a blue semiquinone of the enzyme. Subsequently, the semiquinone decayed by dismutation to form the oxidized and fully reduced forms of the enzyme with a second-order rate constant of 4.4 x 10(4) M-1 s-1. In the presence of equimolar NADP+, the decay of eaq- accompanied an absorption increase at 400 nm, the spectrum of which, formed transiently, is identical to that of NADP radical (NADP.). Subsequently, the transient species decayed concomitantly with the formation of the semiquinone. The rate constant in the formation of the semiquinone was independent of the concentration of the enzyme (6.1 x 10(4) s-1 at pH 7.5). From these results, it is concluded that eaq- reacts with NADP+ bound to the enzyme to form NADP. initially, and subsequently, an electron flows from the NADP. to the flavin by an intracomplex electron transfer. A similar result was obtained in the reaction of CO2- or N-methylnicotinamide radical with the NADP(+)-adrenodoxin reductase complex. These results suggest that the nicotinamide moiety of NADP+ bound to the enzyme is accessible to the solvent and masks the flavin completely.
    No preview · Article · Nov 1995 · Biochemistry
  • Kazuo Kobayashi · Miyako Miki · Seiichi Tagawa
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    ABSTRACT: Using the pulse-radiolysis technique, nitric oxide (NO) was produced by the reaction of an hydrated electron with NO2–. This was verified by the formation of the NO complex of iron(II) myoglobin (Mb) after pulse radiolysis of iron(III) myoglobin in the presence of NO2– under anaerobic conditions. By employing this technique, the reaction of superoxide (O2–) with NO was followed directly in an oxygen-saturated solution containing NO2–. It was found that O2– reacted with NO with a second-order rate constant of 3.8 × 109 dm3 mol–1 s–1 at pH 7.5 to form oxoperoxonitrate(III)[NO(O2)–] which has an absorption maximum around 300 nm. Oxoperoxonitrate(III) thus formed decomposed with a first-order rate constant of 0.8 s–1 at pH 7.5. A similar decay process was observed in the reaction of O2– with NO by monitored stopped-flow, where one part KO2 in dimethyl sulfoxide was mixed with nine parts of a NO-saturated solution in water. The formation of oxoperoxonitrate(III) was complete within the dead-time of the stopped-flow system.
    No preview · Article · Sep 1995 · Journal of the Chemical Society Dalton Transactions
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    ABSTRACT: The crystal structure of cytochrome c2 from Rhodopseudomonas viridis has been refined using molecular dynamics and restrained least-squares methods to a crystallographic R-factor of 0.216 at 2.7 A resolution. A structural comparison between Rps. viridis cytochrome c2 and the other bacterial cytochromes c2 or mitochondrial cytochromes c indicates that the overall protein foldings are very similar to each other with the exception of the surface loop and terminal region of the polypeptide chain. However, the position and hydrogen-bond pattern of the evolutionarily conserved water molecule buried within the heme binding pocket in Rps. viridis cytochrome c2 are common to those in the mitochondrial cytochromes c. This fact indicates that Rps. viridis cytochrome c2 is structurally more similar to mitochondrial cytochromes c than to the other bacterial cytochromes c2.
    Preview · Article · Jun 1994 · FEBS Letters
  • K Miki · S Sogabe · A Uno · T Ezoe · N Kasai · M Saeda · Y Matsuura · M Miki
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    ABSTRACT: An automatic molecular-replacement procedure has been applied to solve the crystal structure of cytochrome c(2) from Rhodopseudomonas viridis. The structure was solved on the basis of the structure of tuna cytochrome c as a search model using an automatic processing program system, AUTOMR. The refinements by molecular dynamics and restrained least-squares methods result in a current crystallographic R factor of 0.219 for diffraction data at 3 A resolution.
    No preview · Article · Jun 1994 · Acta Crystallographica Section D Biological Crystallography
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    ABSTRACT: The reduction of milk xanthine dehydrogenase by salicylate anion radical (SL-), nicotinamide adenine dinucleotide radical (NAD.), and 1-methylnicotinamide (NMA) radicals was investigated by the use of pulse radiolysis. Reduction of the dehydrogenase with SL- proceeded via two phases. From the kinetic difference spectra obtained, the faster and slower phases of reduction represent that of one of the iron-sulfur centers and of FAD, respectively. The rate constant of the faster phase increased with the concentration of the enzyme, suggesting that the reduction follows a bimolecular reaction of SL- with the iron-sulfur center. In contrast, the rate constant of the slower phase (510 s-1) was independent of the concentration of the enzyme at pH 7.5. In order to elucidate the contribution of the molybdenum site in the reaction, a similar reaction was performed with enzyme modified with oxipurinol. In the modified enzyme, the slower phase was lost, whereas the faster phase was not affected. These results suggest that the slower phase is due to intramolecular electron transfer from the molybdenum center to FAD. On the other hand, NAD. reacted predominantly with FAD of the dehydrogenase to form the neutral semiquinone of FAD with a second order rate constant of 1.4 x 10(7) M-1 s-1 at pH 7.5, whereas a similar reaction in the oxidase, which was converted from xanthine dehydrogenase by proteolytical cleavage, was not observed. This suggests that NAD. transfers an electron via the binding site for NAD+ on the dehydrogenase. In contrast, NMA radical reduced only an iron-sulfur center of the dehydrogenase with a second order rate constant of 6.5 x 10(7) M-1 s-1 at pH 7.5.
    Full-text · Article · Dec 1993 · Journal of Biological Chemistry
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    ABSTRACT: Crystals of ferrocytochrome c2 from a non-sulphur purple photosynthetic bacterium, Rhodopseudomonas viridis, have been grown from ammonium sulphate solution at pH 8.5 by the sitting-drop vapour-diffusion procedure. The crystals belong to the trigonal system, space group P3(1)21 (or its enantiomorph P3(2)21) with unit-cell dimensions of a = b = 75.8 A and c = 40.1 A, and diffract to at least 2.0 A resolution. Assuming that an asymmetric unit contains one protein molecule (approx. 12,300 Mr), the solvent content of the crystal is approximately 54.5% (v/v).
    No preview · Article · Nov 1986 · Journal of Molecular Biology
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    Full-text · Article · Nov 1982 · Biotechnology and Bioengineering
  • Yukio Yamamoto · Miyako Miki · Koichiro Hayashi

    No preview · Article · Jan 1981 · Macromolecules
  • Yukio Yamamoto · Miyako Miki · Koichiro Hayashi
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    ABSTRACT: The radiation-induced cationic polymerization of α-methylstyrene has been carried out in several aliphatic and aromatic hydrocarbon solutions in order to study the chain transfer reaction to the solvents. The rate of the chain transfer reaction to C6 aliphatic hydrocarbons is in the order: 2,2-dimethylbutane < 2,3-dimethylbutane < n-hexane − 3-methylpentane. The result has been explained by the fact that the reactivity in hydride transfer increases in the order: primary < secondary < tertiary hydrogens. The activation energy of the chain transfer to n-hexane is 9 kcal/mol higher than that to monomer. The rate of the chain transfer to aromatic hydrocarbons increases in the order: benzene < toluene < m-xylene. It has been suggested that the hydride transfer from the methyl groups of the substituted benzenes occurs as well as the electrophilic substitution of benzene rings.
    No preview · Article · Dec 1980 · Radiation Physics and Chemistry