1986 Fiscal Year Final Research Report Summary
Studies on Retinoid Proteins in Membranes of Halobacterium halobium
| Project/Area Number |
60571012
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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 |
Physical pharmacy
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| Research Institution | Hokkaido University |
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Principal Investigator |
KAMO Naoki Faculty of Pharmaceutical Sciences, Hokkaido University, Associate Prof., 薬学部, 助教授 (10001976)
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| Project Period (FY) |
1985 – 1986
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| Keywords | Halobacterium halobium / Photo-taxis / Poborhodopsin / Photocycle / Sensory rhodopsin / Bacteriorhodopsin / Blue membrane / 光誘起膜電位 |
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| Research Abstract |
(1)Our previous study has shown the existence of the fourth retinoid protein in the cytoplasmic membrane of Halobacterium halobium. We named it as phoborhodopsin (abbreviated as pR). The present study revealed the photocycle of pR with use of flash-photolysis. Upon an illumination, a photochemical intermediate absorbing at 350 nm is formed, which transforms to an intermediate absorbing at 530 nm with a half time of 140 msec at room temperature. The intermediate absorbing at 530 nm decays with a half time of ca 300 msec and returns to the original pR.
(2)H. halobium is attracted to the long wavelength light and this behavior is called positive photo-taxis. In order to prove the hypothesis that the receptor of positive photo-taxis is sensory rhodopsin (sR), we measured carefully the action spectrum of positive photo-taxis and compared it with the absorption spectrum of sR. The finding that both spectra agree well each other supported the hypothesis.
(3)Bacteriorhodopsin (bR) is only protei
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n in purple membrane. When pH of the medium is lowered than 3.2 or when bR is passed through cation exchanger column, bR turns blue. We found that addition of tetrakis(4-fluorophenyl)boron, lipophilic anion to bR formed blue membrane even in neutral solutions. Addition of lipophilic cation to the deionized blue membrane restored the color to purple. Analysis suggested the existence of hydrophobic region where lipophilic ions bind and the electronic charges of this region regulate the color of bR.
(4)One of ways for the estimation of activity of light-driven ion-pumps in the membrane of H. halobium is to measure the photo-induced membrane potential. For small cells or vesicles, indirect method of the estimation of membrane potential should be employed. Distribution of lipophilic ions inside and outside the cells are frequently used. Ambiguity of the estimated values has been suggested which are caused by the binding of lipophilic ions. We developed the method to correct the binding to estimate the true membrane potential. Less
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