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Articles by Mamoru Yamada
Total Records ( 3 ) for Mamoru Yamada
  Pornthap Thanonkeo , Kaewta Sootsuwan , Vichai Leelavacharamas and Mamoru Yamada
  Heat and ethanol had an affect not only on growth and cell viability of an obligatorily fermentative Gram-negative bacterium Zymomonas mobilis, but also on protein synthesis. Analysis by SDS-polyacrylamide gel electrophoresis revealed pronounced increasing of two dominant proteins designated as groES and groEL. Molecular cloning of the gene encoding groES and groEL was performed by PCR technique using specific primers synthesized based on the Z. mobilis groESL gene. Sequencing analysis of 2179 bp led to the detection of two open reading frames encoded for 95 and 549 amino acids, respectively. The deduced amino acid sequence of the Z. mobilis groES and groEL shows a high degree of identity with other. The strongly conserved carboxyl-terminus Gly-Gly-Met motif and two small segments, which appear more conserved between ethanol-producing organisms, were found, suggesting that their may be related to stability of protein under heat or ethanol stress. Induction of groES and groEL occurs in response to heat and ethanol, but not to salt stress.
  Golam Mustafa , Yoshinori Ishikawa , Kazuo Kobayashi , Catharina T. Migita , M. D. Elias , Satsuki Nakamura , Seiichi Tagawa and Mamoru Yamada
  The Escherichia coli membrane-bound glucose dehydrogenase (mGDH) as the primary component of the respiratory chain possesses a tightly bound ubiquinone (UQ) flanking pyrroloquinoline quinone (PQQ) as a coenzyme. Several mutants for Asp-354, Asp-466, and Lys-493, located close to PQQ, that were constructed by site-specific mutagenesis were characterized by enzymatic, pulse radiolysis, and EPR analyses. These mutants retained almost no dehydrogenase activity or ability of PQQ reduction. CD and high pressure liquid chromatography analyses revealed that K493A, D466N, and D466E mutants showed no significant difference in molecular structure from that of the wild-type mGDH but showed remarkably reduced content of bound UQ. A radiolytically generated hydrated electron (Formula) reacted with the bound UQ of the wild enzyme and K493R mutant to form a UQ neutral semiquinone with an absorption maximum at 420 nm. Subsequently, intramolecular electron transfer from the bound UQ semiquinone to PQQ occurred. In K493R, the rate of UQ to PQQ electron transfer is about 4-fold slower than that of the wild enzyme. With D354N and D466N mutants, on the other hand, transient species with an absorption maximum at 440 nm, a characteristic of the formation of a UQ anion radical, appeared in the reaction of Formula, although the subsequent intramolecular electron transfer was hardly affected. This indicates that D354N and D466N are prevented from protonation of the UQ semiquinone radical. Moreover, EPR spectra showed that mutations on Asp-466 or Lys-493 residues changed the semiquinone state of bound UQ. Taken together, we reported here for the first time the existence of a semiquinone radical of bound UQ in purified mGDH and the difference in protonation of ubisemiquinone radical because of mutations in two different amino acid residues, located around PQQ. Furthermore, based on the present results and the spatial arrangement around PQQ, Asp-466 and Lys-493 are suggested to interact both with the bound UQ and PQQ in mGDH.
  Golam Mustafa , Catharina T. Migita , Yoshinori Ishikawa , Kazuo Kobayashi , Seiichi Tagawa and Mamoru Yamada
  Escherichia coli membrane-bound glucose dehydrogenase (mGDH), which is one of quinoproteins containing pyrroloquinoline quinone (PQQ) as a coenzyme, is a good model for elucidating the function of bound quinone inside primary dehydrogenases in respiratory chains. Enzymatic analysis of purified mGDH from cells defective in synthesis of ubiquinone (UQ) and/or menaquinone (MQ) revealed that Q-free mGDH has very low levels of activity of glucose dehydrogenase and UQ2 reductase compared with those of UQ-bearing mGDH, and both activities were significantly increased by reconstitution with UQ1. On the other hand, MQ-bearing mGDH retains both catalytic abilities at the same levels as those of UQ-bearing mGDH. A radiolytically generated hydrated electron reacted with the bound MQ to form a semiquinone anion radical with an absorption maximum at 400 nm. Subsequently, decay of the absorbance at 400 nm was accompanied by an increase in the absorbance at 380 nm with a first order rate constant of 5.7 x 103 s–1. This indicated that an intramolecular electron transfer from the bound MQ to the PQQ occurred. EPR analysis revealed that characteristics of the semiquinone radical of bound MQ are similar to those of the semiquinone radical of bound UQ and indicated an electron flow from PQQ to MQ as in the case of UQ. Taken together, the results suggest that MQ is incorporated into the same pocket as that for UQ to perform a function almost equivalent to that of UQ and that bound quinone is involved at least partially in the catalytic reaction and primarily in the intramolecular electron transfer of mGDH.
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