Rhodopsin and bacteriorhodopsin

There has been extensive work done on myoglobin, haemoglobin, Cytocln-ome-c, rhodopsin and bacteriorhodopsin. In fact, there are literally hundreds of articles on each of the above subjects. Flere we will consider haemoglobin [12]. The first tliree of these examples are based on the protohaeme unit, shown in figure Bl.2.10. 

It triggers conformational changes in retinoid proteins, such as rhodopsin and bacteriorhodopsin, relevant to vision and ATP synthesis, respectively. 

Birge, R. R., Nature of the primary photochemical events in rhodopsin and bacteriorhodopsin. Biochim. Biophys. Acta 1016 293, 1990. A review covering rhodopsin s structure, spectroscopic properties and responses to light. This article also discusses the closely related protein, bacteriorhodopsin, which serves as a light-driven proton pump in halo-philic bacteria. 

UC Chemical Shift-Conformation Relationship in the Chromophores of Rhodopsin and Bacteriorhodopsin... 

The chromophores of rhodopsin and bacteriorhodopsin are 11 -cis- and all-trans-retinal Schiff bases, respectively. Upon binding to the proteins, their unsaturated carbons show anomalous 13C chemical shifts compared with those of corresponding model compounds. This indicates the occurrence of interactions between the chromophore and its surrounding protein matrix. Ab inito shielding calculation reveals that the major part of such anomalous shifts originates in the conformational change of the chromophore. 

Boynton, R. (1979) Human Color Vision Holt, Rinehart Winston, pg 156, comment to footnote 9. 7Birge, R. (1981) Photophysics oflight transduction in rhodopsin and bacteriorhodopsin. Ann. Rev. Biophys. Bioeng. Vol. 10, pp 315-354... 

CD Spectra. In spite of their being twisted about the C -Cj single bond (262,263), retinal isomers have no optical activity in solution, presumably because of the presence of comparable amounts of both enantiomers of each of the twisted forms. However, both rhodopsin and bacteriorhodopsin are optically active in their visible and uv transitions. The origin of the optical activity in rhodopsin (264-276) is still subject to speculation. 

Nakanishi K, Zhang H, Lerro KA, Takekuma S, Yamamoto T, Lien TH, Sastry L, Back D-J, Moquin-Pattey C, Boehm MF, Derguini F, Gawinowicz MA (1995) Photoaffinity labeling of rhodopsin and bacteriorhodopsin. Biophys Chem 56 13-22... 

Intramolecular heavy atom effects influence the photoisomerization derivatives of 5,5-diphenyl-1,3-cyclohexadiene The homogeneous acid catalysis of the photoisomerization of trans-3-(2-hydroxy-benzylidene)-4,5-dihydrofuran-2(3H)-one and model mechanisms for isomerization of carbocyanines have both been analyzed. The process of photoisomerization of the biologically important rhodopsin and bacteriorhodopsin has been examined by a theoretical ab initio study of retinal analogues. ... 

The kinetics of the photoisomerization of bilirubin has been studied because of the relevance to phototherapy. The fluorescence of bilirubin increases on binding to human serum albumin. This and other primary photoprocesses have been investigated by picosecond spectroscopy. Karvaly has put forward a new photochemical mechanism for energy conversion in bacteriorhodopsin. An extensive review of the photophysics of light transduction in rhodopsin and bacteriorhodopsin has been made by Birge. The dynamics of cis-trans isomerization in rhodopsin has been analysed by INDO-CISD molecular orbital theory. Similar calculations on polyenes and cyanine dyes have also been reported. A new picosecond resonance Raman technique shows that a distorted... 

From the beginning of research into retinoids, absorption spectroscopy has been employed as an aid in the characterization of structure (Zechmeister, 1962 Vetter et aL, 1971), and the principles and possible applications of this spectroscopic method have been discussed in detail in review articles (Drujan, 1971 Ottolenghi, 1980). It has proved particularly useful in the investigation of the protein pigments rhodopsin and bacteriorhodopsin (Honig and Ebrey, 1974 Honig et aL, 1975 Honig, 1978 Stoeckenius et aL, 1979). 

Infrared spectroscopy (IR) has not been extensively used in retinoid analysis (17,18). However, the newer techniques of Resonance Raman and infrared-difference spectroscopy have been applied to retinal proteins m rhodopsin and bacteriorhodopsin. By use of these techniques, it is possible to determine the structures of the chromophores m the visual pigments and in the intermediates of their photoreactions Also, it is possible to study the interactions between the chromophores and the protein, and the structural changes evoked in the protein by the photoreaction (1,19). 

Even though rhodopsin and bacteriorhodopsin appear to differ fundamentally in their function, mode of action, structure, and photochemistry, it has been suggested (Stoeckenius et ai, 1979) that the two proteins did not evolve independently. One possibility is that the halobacteria may have acquired bacteriorhodopsin by gene transfer from a eukaryote (Stoeckenius et al., 1979). However, a preliminary report by Hargrave et al. (1983) claims that no statistically significant sequence homology can be found. Thus, the resemblance between these proteins appears to be only superficial. 

Extensive arguments, based on absolute quantum yield values as well as on their temperature and wavelength dependence, have been previously presented showing that the primary event in both rhodopsin and bacteriorhodopsin is controlled by the quantitative population of a common excited state minimum along the coordinate between the... 

For a clarification of the above questions we have carried out calculations of spectroscopic transition energies and oscillator strengths for a model all-trans bacteriorhodopsin molecule. As required by the Resonance Raman data for both rhodopsin and bacteriorhodopsin we have assumed that in BR y the Schiff base nitrogen is fully protonated. This assumption constitutes the basis of models a. and c, but not of model where full protonation is claimed only for the bathophotoproducts, J525 bathorhodopsin. 

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