BIOSYNTHETIC INCORPORATION OF M-FLUOROTYROSINE INTO BACTERIORHODOPSIN |
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Authors: | E Starr Hazard III Rajni Govindjee Thomas G Ebrey Rosalie K Crouch |
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Institution: | Department of Ophthalmology, Medical University of South Carolina, Charleston 29425-2501. |
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Abstract: | Halobacterium halobium, grown in a defined medium where tyrosine had been largely replaced with m-fluorotyrosine, biosynthetically produced purple membrane. Analysis of this membrane by high pressure liquid chromatography of phenylthiocarbamyl derivatized amino acids of membrane acid hydrolysates revealed that up to 50% of the tyrosine was present as the m-fluorotyrosine form. Yields of the purple membrane decreased as the level of incorporation increased. The experimental purple membrane showed a single 19F NMR resonance at -61.983 ppm (relative to trifluoroacetic acid). The bacteriorhodopsin (bR) in the purple membrane was normal as assayed by gel electrophoresis, isoelectric focusing, circular dichroic spectra, and UV-visible spectra. However, the fluorinated tyrosine bacteriorhodopsins at near neutral pH exhibited slightly slower rates of proton uptake and a slower M-state decay with biphasic kinetics reminiscent of alkaline solutions of bR (pH > 9). These results imply that the tyrosines in bacteriorhodopsin may play a role in the photoactivated proton translocation process of this pigment. |
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