| Project/Area Number |
62480125
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
General medical chemistry
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| Research Institution | Kyoto University |
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Principal Investigator |
ORII Yutaka Faculty of Medicine, Kyoto University, 医学部, 助教授 (60028149)
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| Co-Investigator(Kenkyū-buntansha) |
SANO Seiyo Shiga University of Medical Sciences, 学長 (60025533)
YOSHINAGA Takeo Faculty of Medicine, Kyoto University, 医学部, 助手 (30025663)
KAWANISHI Shosuke Faculty of Medicine, Kyoto University, 医学部, 講師 (10025637)
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| Project Period (FY) |
1987 – 1988
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| Project Status |
Completed (Fiscal Year 1988)
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| Budget Amount *help |
¥5,900,000 (Direct Cost: ¥5,900,000)
Fiscal Year 1988: ¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1987: ¥3,900,000 (Direct Cost: ¥3,900,000)
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| Keywords | heme degradation / oxyprotoheme / NADPH-cytochrome c reductase / photosensitizer / singlet oxygen / チトクロム酸化酵素 / 一重項酵素 / NADPHーチトクロムC還元酵素 |
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| Research Abstract |
The reaction mechanism of conversion of oxyprotoheme IX to verdohemochrome IX in heme degradation was investigated by employing purified preparations of heme oxygenase and NADPH-cytochrome c reductase in homogeneous state and synthetic -oxyprotoheme IX and its isomers. The reaction was followed kinetically as difference spectral changes and the reaction products were analyzed by HPLC.
Spectral examinations and product analyses clearly demonstrated that only -isomer of oxyprotoheme IX was degraded efficiently to biliverdin IX. In the reconstituted reconstituted reaction system K_m for -oxyprotoheme IX was 3.6 Malthough this was almost two-fold that for the natural substrate, protoheme IX. The rate of conversion of -oxyprotoheme IX to biliverdin IX was two times faster than that of protoheme IX. These kinetic parameters strongly support a previous proposal that -oxyprotoheme IX is an intermediate during heme degradation.
The activity of bovine heart cytochrome oxidase decreased when the enzyme was illuminated in the presence of protoporphyrin IX under aerobic conditions. The photoinactivation of the enzyme was dependent on the protoporophyrin concentration andillumination time, but the photodynamic effect was not observed under atmosphere of 100% nitrogen. The generation of singlet oxygen was confirmed by ESR spectroscopy as the appearance of nitroxide radical from 2,2,6,6-tetramethyul-4-peperidone. Scavengers of singlet oxygen like histidine, GMP or DABCO were effective in preventing the enzyme from photoinactivation. Thus singlet oxygen was concluded to be deleterious to cytochrome oxidase and degrade heme a moiety as revealed by spectral examinations.
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