• 제목/요약/키워드: FBR

검색결과 89건 처리시간 0.022초

Positron Annihilation Study of Vacancy Type Defects in Ti, Si, and BaSrFBr:Eu

  • Lee, Chong Yong
    • Applied Science and Convergence Technology
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    • 제25권5호
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    • pp.85-87
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    • 2016

  • Coincidence Doppler broadening and positron lifetime methods in positron annihilation spectroscopy has been used to analyze defect structures in metal, semiconductor and polycrystal, respectively. The S parameter and the lifetime (${\tau}$) value show that the defects were strongly related with vacancies. A positive relationship existed between the scanning electron microscope (SEM) images and the positron annihilation spectroscopy (PAS). According to the SEM images and PAS results, measurements of the defects with PAS indicate that it was more affected by the defect than the purity.

  • https://doi.org/10.5757/ASCT.2016.25.5.85 인용 PDF KSCI

Identification of Amino Acid Residues Involved in Feedback Inhibition of the Anthranilate Synthase in Escherichia coli

  • Kwak, Joon-Hyeok;Hong, Kwang-Won;Lee, Sung-Haeng;Hong, Jin-Han;Lee, Se-Yong
    • BMB Reports
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    • 제32권1호
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    • pp.20-24
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    • 1999

  • The first step of the branch pathway in tryptophan biosynthesis is catalyzed by anthranilate synthase, which is subjected to feedback inhibition by the end product of the pathway. The $trpE^{FBR}$ gene from a mutant Escherichia coli strain coding for anthranilate synthase that was insensitive to feedback inhibition by tryptophan has been cloned. To identify the amino acid changes involved in the feedback regulation of anthranilate synthase, the nucleotide sequence of the mutant $trpE^{FBR}$ gene was determined. Sequence analysis of the $trpE^{FBR}$ gene revealed that four bases were changed in the structural gene while alteration was not found in the 5' control region. Among these base changes, only two base substitutions caused the alterations in amino acid sequences. From the results of restriction fragment exchange mapping, the 61st nucleotide, C to A substitution, that changed $Pro^{21}{\rightarrow}Ser$ was identified as the cause of the desensitization to feedback inhibition by tryptophan. Additional feedback-resistant enzymes of the E. coli anthranilate synthases were constructed by site-directed mutagenesis to examine the effect of the $Ser^{40}\;{\rightarrow}\;Arg^{40}$ change found in the $trpE^{FBR}$ gene of Brevibacterium lactofermentum. From the feedback inhibition analysis, the $Pro^{21}{\rightarrow}Ser$ and $Ser^{40}{\rightarrow}Arg$ mutants maintained about 50% and 90% of their maximal activities, respectively, even at the extreme concentration of 10 mM tryptophan. From these results, we suggest that the $Pro^{21}$ and $Ser^{40}$ residues are involved in the tryptophan binding in the E. coli enzyme.

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