Biosynthetic incorporation of m-fluorotyrosine into bacteriorhodopsin.
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.
Hazard
E S
ES
Department of Ophthalmology, Medical University of South Carolina, Charleston 29425-2501.
Govindjee
R
R
Ebrey
T G
TG
Crouch
R K
RK
D001436:Bacteriorhodopsins / Q000096:biosynthesis* / Q000737:chemistry; D019617:Halobacterium salinarum / Q000378:metabolism; D010777:Photochemistry; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
C001245:3-fluorotyrosine; D014443:Tyrosine; D001436:Bacteriorhodopsins