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ROLE OF HYDROXYL‐BEARING AMINO ACIDS IN DIFFERENTIALLY TUNING THE ABSORPTION SPECTRA OF THE HUMAN RED AND GREEN CONE PIGMENTS
Author(s) -
Merbs Shannath L.,
Nathans Jeremy
Publication year - 1993
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1993.tb04956.x
Subject(s) - pigment , chemistry , bearing (navigation) , cone (formal languages) , absorption (acoustics) , photochemistry , absorption spectroscopy , amino acid , biochemistry , organic chemistry , optics , physics , computer science , algorithm , astronomy
The human red and green cone pigments differ at either 15 or 16 amino acids, depending upon which polymorphic variants are compared. Seven of these amino acid differences involve the introduction or removal of a hydroxyl group. One of these differences, a substitution of alanine for senne at position 80, was found previously to produce a 5 nm blue shift. To determine the role of the remaining six hydroxyl group differences in tuning the absorption spectra of the human red and green pigments, we have studied six site‐directed mutants in which single amino acids from the green pigment have been substituted for the corresponding residues in the red pigment. Blue shifts of 7 and 14 nm were observed upon substitution of phenylalanine for tyrosine at position 277 and alanine for threonine at position 285, respectively. Single substitutions at positions 65, 230, 233, and 309 produced spectral shifts of 1 nm or less. These data are in good agreement with a model based upon sequence comparisons among primate pigments and with the properties of site‐directed mutants of bovine rhodopsin. Nonadditive effects observed in comparing the absorption spectra of red‐green hybrid pigments remain to be explained.