FTIR study of carboxylic acids and tyrosines in bacteriorhodopsin
Lin, Shuo-Liang
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https://hdl.handle.net/2142/23914
Description
Title
FTIR study of carboxylic acids and tyrosines in bacteriorhodopsin
Author(s)
Lin, Shuo-Liang
Issue Date
1988
Doctoral Committee Chair(s)
Gratton, E.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
FTIR study
carboxylic acids
tyrosines
bacteriorhodopsin
infrared spectra
photoreaction
amino acid residues
Language
en
Abstract
High quality infrared difference spectra of bacteriorhodopsin (bR) were obtained in order to study its photoreaction at the molecular level. The noise level was near 10-5 in the spectral regions where amino acid residues are monitored. The excellent signal to noise ratio allowed detection of absorption changes of single amino acids during the photoreaction. Aspartic acids and glutamic acids in bR were monitored by 13C labeling. Tyrosines were monitored by both 2H and nitrate substitution. Some of the amino acid band regions were decomposed by curve fitting. Alteration of absorption bands among individual bR states were found for aspartic acids and tyrosines, but were not found for glutamic acids. These changes are interpreted as a change in protonation of at least two aspartic acids and one tyrosine. In addition one aspartic acid and one tyrosine were subject to environmental perturbation. Nitration of tyrosines indicates that none of the tyrosine spectral changes occurring during the photoreaction cycle can be attributed to tyrosine-26 or tyrosine-64. A model based on intramolecular interaction is built to elucidate the spectral change observed during the cycle. This model places the three aspartic acids and the two tyrosines near the chromophore of bR. One aspartic acid and one tyrosine, together with a hypothetical positive charge, are postulated to form the primary environment around the Schiff base of the chromophore. These residues adjust conformation during the photoreaction. Another aspartic acid interacts with the Schiff base after the chromophore 13-cia isomerization. The nature of the environmental perturbation is discussed for individual residues. Also discussed in the thesis are the quality control in FTIR spectroscopy, prospective experiments, the
present finding's implication to the mechanism of the color regulation and proton pumping of bR, and the general structure-function relationship of opsins.
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