title: Evidence for a carboxyl group in the vicinity of the retinal chromophore of bacteriorhodopsin.
abstract: Carboxyl groups of bacteriorhodopsin in purple membranes were activated using a hydrophobic reagent and then covalently labeled with a pH-sensitive reporter group, nitrotyrosine methyl ester. The membrane-bound reporter group had different spectral properties, and a pK 3 units higher than in solution. In purple membranes, an isosbestic point between the 428nm absorption peak of nitrotyrosine methyl ester, and the bacteriorhodopsin 570nm chromophore seen in alkaline titration, indicated interactions between the reporter group and retinal. Modification of white membranes (bacterioopsin from R1mW strain) revealed similar, unusual spectral and ionization properties. Thus, the hydrophobic environment, not retinal interactions per se, are responsible for the ionization behavior of the reporter group. These results indicate that a carboxyl group is near the retinal chromophore of bacteriorhodopsin.
mesh_terms: D001436:Bacteriorhodopsins / Q000378:metabolism*; D002338:Carotenoids / Q000378:metabolism*; D002942:Circular Dichroism; D006217:Halobacterium / Q000378:metabolism; D007700:Kinetics; D011487:Protein Conformation; D012172:Retinaldehyde / Q000378:metabolism*; D013053:Spectrophotometry; D014443:Tyrosine / Q000031:analogs & derivatives; D014801:Vitamin A / Q000031:analogs & derivatives*
chemical_list: D014801:Vitamin A; C038390:2-nitrotyrosine methyl ester; D002338:Carotenoids; D014443:Tyrosine; D001436:Bacteriorhodopsins; D012172:Retinaldehyde