Light-driven protonation changes of internal aspartic acids of bacteriorhodopsin: an investigation by static and time-resolved infrared difference spectroscopy using 4-/sup 13/Caspartic acid labeled purple membrane
The molecular events during the photocycle of bacteriorhodopsin have been studied by the method of time-resolved and static infrared difference spectroscopy. Characteristic spectral changes involving the C=O stretching vibration of protonated carboxylic groups were detected. To identify the corresponding groups with either glutamic or aspartic acid, BR was selectively labeled with (4-/sup 13/C)aspartic acid. An incorporation of ca. 70% was obtained. The comparison of the difference spectra in the region of the CO/sub 2/- stretching vibrations of labeled and unlabeled BR indicates that ionized aspartic acids are influenced during the photocycle, the earliest effect being observed already at the K610 intermediate. Taken together, the results provide evidence that four internal aspartic acids undergo protonation changes and that one glutamic acid, remaining protonated, is disturbed. The results are discussed in relation to the various aspects of the proton pumping mechanism, such as retinal isomerization, charge separation, pK changes, and proton pathway.
- Research Organization:
- Universitaet Freiburg, Germany, F.R.
- OSTI ID:
- 5520650
- Journal Information:
- Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 24:2; ISSN BICHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
59 BASIC BIOLOGICAL SCIENCES
AMINO ACIDS
ASPARTIC ACID
BACTERIA
BIOCHEMICAL REACTION KINETICS
CARBON 13
CARBON ISOTOPES
CARBOXYLIC ACIDS
EVEN-ODD NUCLEI
INFRARED SPECTRA
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
LABELLED COMPOUNDS
LIGHT NUCLEI
MEMBRANE TRANSPORT
MEMBRANES
MICROORGANISMS
NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
PHOTOSYNTHETIC MEMBRANES
PIGMENTS
PROTEINS
REACTION KINETICS
RHODOPSIN
SPECTRA
SPECTROSCOPY
STABLE ISOTOPES
TRACER TECHNIQUES