| Project/Area Number |
61580145
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
物質生物化学
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| Research Institution | Okayama University |
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Principal Investigator |
TSUCHIYA Tomofusa Okayama University, Professor, 薬学部, 教授 (80012673)
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| Co-Investigator(Kenkyū-buntansha) |
TSUDA Masaaki Okayama University, Associate Professor, 薬学部, 助教授 (80132736)
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| Project Period (FY) |
1986 – 1987
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| Project Status |
Completed (Fiscal Year 1987)
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| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1987: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1986: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Keywords | Transport carrier / Primary structure / Amino acid substitution / Changes in function / カチオン共役 / 一次構造の変化 / 機能の変化 / 変異の同定 |
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| Research Abstract |
Several transport systems for nutrients in cell membranes are Na^+-coupled cotransport systems. One of the best characterized Na^+-coupled cotransport systems is the melibiose transport system in Esherichia coli.
We isolated many mutants which showed altered cation specificity in the melibiose carrier. There were two types of mutant. The melibiose carrier of one type of the mutants lost the ability to couple to H^+ and acquired the ability to couple to Li^<> when melibiose was the substrate. The coupling to Na^+ in those mutants was normal. The melibiose carrier of another type of the mutants lost the ability to couple to H^<> and could utilize only Na^+ as the coupling csation. We analysed the second type mutants in this project.
Mutated gene, melB, of the mutants was cloned, and the nucleotide sequence was determined. The nucleotide replacements caused the following substitutions of amino acid residues in the melibiose carrier; Pro-142 with Ser, Leu-232 with Phe, or Ala-236 with Thr or Val. These amino acid residues are located in slightly hydrophobic regions of the melibiose carier. The results provide a strong support for the idea that such regions or their vicinities which contain those amino acid residues play an important role in H^+ recognition or H^+ transport by the melibiose carrier.
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