Lavoisier S Ramos

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For visual pigments, a covalent bond between the ligand (11-cis-retinal) and receptor (opsin) is crucial to spectral tuning and photoactivation. All photoreceptors have retinal bound via a Schiff base (SB) linkage, but only UV-sensitive cone pigments have this moiety unprotonated in the dark. We investigated the dynamics of mouse UV (MUV) photoactivation,(More)
The photochemical and subsequent thermal reactions of the mouse short-wavelength visual pigment (MUV) were studied by using cryogenic UV-visible and FTIR difference spectroscopy. Upon illumination at 75 K, MUV forms a batho intermediate (lambda(max) approximately 380 nm). The batho intermediate thermally decays to the lumi intermediate (lambda(max)(More)
Boron-dipyrrin chromophores containing a 5-aryl group with or without internal steric hindrance toward aryl rotation have been synthesized and then characterized via X-ray diffraction, static and time-resolved optical spectroscopy, and theory. Compounds with a 5-phenyl or 5-(4-tert-butylphenyl) group show low fluorescence yields (approximately 0.06) and(More)
The absorption maximum of blue proteorhodopsin (BPR) is the most blue-shifted of all retinal proteins found in archaea or bacteria, with the exception of sensory rhodopsin II (SRII). The absorption spectrum also exhibits a pH dependence larger than any other retinal protein. We examine the structural origins of these two properties of BPR by using optical(More)
Xenopus violet cone opsin (VCOP) and its counterion variant (VCOP-D108A) are expressed in mammalian COS1 cells and regenerated with 11-cis-retinal. The phototransduction process in VCOP-D108A is investigated via cryogenic electronic spectroscopy, homology modeling, molecular dynamics, and molecular orbital theory. The VCOP-D108A variant is a UV-like pigment(More)
Visual pigments are G-protein-coupled receptors that provide a critical interface between organisms and their external environment. Natural selection has generated vertebrate pigments that absorb light from the far-UV (360 nm) to the deep red (630 nm) while using a single chromophore, in either the A1 (11- cis-retinal) or A2 (11- cis-3,4-dehydroretinal)(More)
Assignment of the protonation state of the residue Glu-181 is important to our understanding of the primary event, activation processes and wavelength selection in rhodopsin. Despite extensive study, there is no general agreement on the protonation state of this residue in the literature. Electronic assignment is complicated by the location of Glu-181 near(More)
The role of the extracellular loop region of a short-wavelength sensitive pigment, Xenopus violet cone opsin, is investigated via computational modeling, mutagenesis, and spectroscopy. The computational models predict a complex H-bonding network that stabilizes and connects the EC2-EC3 loop and the N-terminus. Mutations that are predicted to disrupt the(More)
The photochemistry of the 13-desmethyl (DM) analogue of bacteriorhodopsin (BR) is examined by using spectroscopy, molecular orbital theory, and chromophore extraction followed by conformational analysis. The removal of the 13-methyl group permits the direct photochemical formation of a thermally stable, photochemically reversible state, P1(DM) (lambda(max)(More)
Seven perylene-porphyrin dyads were examined with the goal of identifying those most suitable for components of light-harvesting systems. The ideal dyad should exhibit strong absorption by the perylene in the green, undergo rapid and efficient excited-state energy transfer from perylene to porphyrin, and avoid electron-transfer quenching of the porphyrin(More)
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