393 research outputs found
Chiral phase transition of bulk Abelian gauge theories in the Randall-Sundrum brane world
The chiral phase transition of strong-coupling Abelian gauge theories is
investigated in the brane world. It is assumed that gauge boson propagates in
an extra dimension, i.e. bulk gauge theories. The phase structure is
analytically evaluated by using the low-energy effective theories. We also
numerically solve the ladder Schwinger-Dyson equation for the full fermion
propagator including Kaluza-Klein (KK) excitation modes of the gauge field. It
is found that the chiral phase transition is of the second order, and the
critical value of the coupling constant is obtained. The extra dimension has a
large influence on the chiral phase transition for the Randall-Sundrum (RS)
brane world. It is studied how the number of KK modes affect the chiral phase
transition.Comment: 18 pages, 7 figures, REVTe
Structure of Chiral Phase Transitions at Finite Temperature in Abelian Gauge Theories
The mechanism of the chiral symmetry breaking is investigated in the
strong-coupling Abelian gauge theories at finite temperature. The
Schwinger-Dyson equation in Landau gauge is employed in the real time formalism
and is solved numerically within the framework of the instantaneous exchange
approximation including the effect of the hard thermal loop for the photon
propagator. It is found that the chiral symmetry is broken below the critical
temperature T for sufficiently large coupling. The chiral phase transition is
found to be of the 2nd order and the phase diagram on the plane is
obtained. It is investigated how the structure of the chiral phase transition
is affected by the hard thermal loops in the photon propagator.Comment: 15pages, uses epic.sty and eepic.st
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The isozymes of mammalian thioredoxin reductase (TrxR) contain the penultimate selenocysteineresidue (SeCys) in the redox-active C-terminal tetrapeptide, -Gly-Cys-SeCys-Gly (end). Amutant form of the mammalian enzyme TrxR-X498C in which SeCys is replaced with Cys showsa dramatically decreased catalytic activity, suggesting that SeCys residue plays an integral role inthe catalysis. In contrast, TrxR of the fruit fly, Drosophila melanogaster, has no selenium in the corresponding C-terminal redox sequence, which instead of SeCys has flanking serine residues in the terminal sequence, -Ser-Cys-Cys-Ser (end). Because the catalytic activity of Dm-TrxR is comparable to that of the mammalian selenoenzyme, we introduced the serine residues at the corresponding positions of the recombinant TrxR-X498C and mimicked the redox center of the fruit fly TrxR. However, the catalysis remained as low as the Cys mutant of the selenoenzyme,
suggesting that the additional structural features are still required for the tetrapeptide to function as a redox center. MOPAC calculation suggested that the complete motif might involve the hexapeptide sequence, which includes a proline residue, -Pro-X-Ser-Cys-Cys-Ser (end). The proline-containing motif is conserved among other insect TrxRs such as those of honeybee and fruit fly.ã»ä¹³é¡ããªã¬ããã·ã³éå
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Purification and Characterization of l-Methionine Decarboxylase from Streptomyces sp. 590
L-Methionine decarboxylase [EC 4.1.1.57] catalyzes the decarboxylation of L-methionine and is a pyridoxal 5â-phosohate(PLP)-dependent enzyme. L-Methionine decarboxylase has been purified 630-fold by DEAE-Toyopearl 650M, Phenyl-Toyopearl 650M and Sephacryl S-300 column chromatographies from Streptomyces sp.590. The enzyme has a dimeric structure with identical subunits of Mr 60,000. This enzyme shows optimum activity at pH7.0 and 45°C, and is stable between pH5.7 and pH9.0. L-Methionine decarboxylase has antitumor activity against RERF-LC-AI and HeLa cells. Ten N-terminal amino acid sequence of L-methionine decarboxylase was determined, and the sequence showed no homology with other reported proteins
Identification of Ornithine-lactam Converted from Arginine in Streptomyces incarnatus NRRL8089
Sinefungin is a nucleoside antibiotic, in which a molecule of L-ornithine is linked to the 5' end of adenosine through a C-C bond. The antibiotic was isolated from the culture broth of Streptomyces incarnatus. For the purpose of detecting intermediate of sinefungin biosynthesis, resting cell suspensions were incubated with supplemental L-arginine, and L-ornithine. 50mM Arginine was converted to a compound X that has low polarity. 50mM ornithine was not converted and remained in reaction solution. Compound X was purified using HPLC, and analyzed using (1)H-NMR and FAB-MS. These analyses showed that a compound X is "ornithine-lactam" (MwïŒ114), which has a structure of circularized ornithine. These results indicated that S. incarnatus has an enzyme that converts arginine to ornithine-lactam. Such an enzyme has never been reported, and suggested that it may be relevant to sinefungin biosynthesis.ã·ããã³ã®ã³ã¯æçèïŒæãã©ãªã¢æŽ»æ§ãæããæ žé
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Semiempirical molecular orbital calculation (MOPAC) was used to estimate the enthalpy difference (ÎH) between the reduce and oxidized states of the C-terminal rebox center of human thioredoxin reductase. Heat of formation was computed by WinMOPAC 3.5Pro for the model peptides, N-Acetyl-Ser-Ile-Leu-Gly-X1-X2-Gly, whose-X1-X2-sequence was-Cys SeCys-(natural sequence), -SeCys-Cys-(reverse sequence), -Cys-Cys, and-SeCys-SeCys-. Calculation by Hamiltonian AM1 and PM3 agreed that the oxidized state with selenosulfide bonds and a diselenide bond were more favoralbe than their reduced states. Only the peptide that contained-Cys-Cys-sequence was shown to have lower enthalpy when the two Cys were in the reduced form. It has been reported that substitution of SeCys498 to Cys results in the mujtant TrxRs retaining only about 1% of the enzyme activity. The results of computational estimation supported the experimental hypothesis that the inactivation by SeCys498Cys mutation was due to the unfavorable formation of disulfide bond between Cys497-Cys498.ããã®ããªã¬ããã·ã³éå
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Screening Isolation and Characterization of Thermophilic and Acidophilic Bacteria
We have isolated 53 thermophilic and acidophilic bacteria from about 150 samples from acidic hot springs. All the strains isolated exhibited growth only at high temperatures and low pH ranges. We extensively characterized the strain UZ-1 which was isolated from Unzen spa. This strain was found to be a gram-negative, aerobic and heterotrophic bacterium. The DNA base composition was 63 mol% GC. Growth occurs over a range of 37â to 65â with an optimum temperature of 60â, and between pH 2.0 and pH 6.0 with an optimum pH of 3.0. On the other hand, the optimum temperature of the other 6 isolated strains was 70â. We report, in this paper, the characteristics of the isolated strains.æã
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Isolation,Identification and Characterization of the Aminoacylase Inhibitors from Actinomycetes
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