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  • Title: A covalent link between the chromophore and the protein backbone of bacteriorhodopsin is not required for forming a photochemically active pigment analogous to the wild type.
    Author: Friedman N, Druckmann S, Lanyi J, Needleman R, Lewis A, Ottolenghi M, Sheves M.
    Journal: Biochemistry; 1994 Mar 01; 33(8):1971-6. PubMed ID: 8117653.
    Abstract:
    Bacteriorhodopsin pigments lacking the retinal-Lys-216 covalent bond were prepared by reconstituting the K216G mutant protein with retinal alkylamine Schiff bases. The procedure follows the approach of Zhukovsky et al. [Zhukovsky, E., Robinson, P., & Oprian, D. (1991) Science 251, 558-560] in the case of visual (rhodopsin) pigments. Reconstitution leads to a mixture of three pigments. One of them, bR(K216G)/566a, absorbs (pH = 6.9) at 566 nm. Its absorption is pH-dependent, exhibiting a purple to blue transition. The pigment's laser-induced photocycle patterns are similar to those of wild-type all-trans-bR. A second component, bR(K216G)/566b, exhibits an independent photocycle reminiscent of that of wild-type 13-cis-bR. A third pigment component, bR(K216G)/630, absorbs around 630 nm. Experiments in the presence of a pH dye indicator show that illumination of bR(K216G)/566 produces a detectable proton gradient. It is concluded that a covalent bond between the retinal chromophore and the protein backbone is not a prerequisite for the basic structure and photochemical features of bR or for its proton pump activity.
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