2000 Fiscal Year Final Research Report Summary
Structures and functions of metalloflavoenzymes which produce free radicals
| Project/Area Number |
09480167
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| Research Category |
Grant-in-Aid for Scientific Research (B).
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Functional biochemistry
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| Research Institution | NIPPON MEDICAL SCHOOL |
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Principal Investigator |
NISHINO Takeshi NIPPON MEDICAL SCHOOL, BIOCHEMISTRY AND MOLECULAR BIOLOGY, Professor, 医学部, 教授 (40094312)
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| Co-Investigator(Kenkyū-buntansha) |
OKAMOTO Ken NIPPON MEDICAL SCHOOL, BIOCHEMISTRY AND MOLECULAR BI0LOGY, Assistant, 医学部, 助手 (60267143)
MATSUMURA Tomohiro NIPPON MEDICAL SCHOOL, BIOCHEMISTRY AND MOLECULAR BIOLOGY, Assistant, 医学部, 助手 (20297930)
IWASAKI Toshio NIPPON MEDICAL SCHOOL, BIOCHEMISTRY AND MOLECULAR BIOLOGY, Lecturer, 医学部, 講師 (40277497)
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| Project Period (FY) |
1997 – 2000
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| Keywords | reactive oxygen species / xanthine dehydrogenase / xanthine oxidase / niric oxide synthase / metallo-protein / non-heme iron / peroxiredoxin / heme binding protein |
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| Research Abstract |
Xanthine dehydrogenase/oxidase and nitric acid synthetase are complex flavoprotein that produce free radicals. In this study, we presented the crystal structure of the dimeric (Mr 290,000) bovine milk XDH at 2.1 Å resolution and XO at 2.5 Å resolution and describe the major changes that occur upon the proteolytic transformation of XDH to the XO form. Each molecule is composed of an N-terminal 20 kDa domain containing two iron sulfur centers, a central 40 kDa FAD domain, and a C-terminal 85 kDa molybdopterin-binding domain with the four redox centers aligned in an almost linear fashion. Cleavage of surface-exposed loops of XDH causes major structural rearrangement of another loop close to the flavin ring (Gin-423-Lys-433). This movement partially blocks access of the NAD substrate to the FAD cofactor and changes the electrostatic environment of the active site, reflecting the switch of substrate specificity observed for the two forms of this enzyme. We have also constructed several mutant enzyme of rat liver XDH and determined the character to confirm the responsible residues for conversion.
We have expressed mouse neuronal nitic acid synthase (NOS) as well as the iso-form of natural mutant and determined characters of the enzymes by several physicochemical methods. We have also studied some other related enzymes such as heme containing flavo-protein, cellobiose dehydrogenase, and heme binding protein, HBP23 has peroxidase activity.
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