Rhodopsins Bacteriorhodopsins

Optically induced cis-trans isomerization is a key structural dynamic element for many types of photochromic switches as stilbenes and azobenzene derivatives and for photosensor proteins as bacteriorhodopsin, rhodopsin, and photoactive yellow protein. 

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. 

Shreve A P and Mathies R A 1995 Thermal effects in resonance Raman-scattering—analysis of the Raman intensities of rhodopsin and of the time-resolved Raman-scattering of bacteriorhodopsin J. Phys. Chem. 99 7285-99... 

FIGURE 2.3 The three main families of mammalian G-protein-coupled 7TM receptors in mammals. No obvious sequence identity is found between the rhodopsin-like family A, the glucagon/VIP/calcitonin family B, and the metabotropic glutamate/chemosensor family C of G-protein-coupled 7TM receptors, with the exception of the disulfide bridge between the top of TM-III and the middle of extracellular loop-2 (see Figure 2.2). Similarly, no apparent sequence identity exists among members of these three families and, for example the 7TM bitter taste receptors, the V1R pheromone receptors, and the 7TM frizzled proteins, which all are either known or believed to be G-protein-coupled receptors. Bacteriorhodopsins, which are not G-protein-coupled proteins but proton pumps, are totally different in respect to amino-acid sequence but have a seven-helical bundle arranged rather similarly to that for the G-protein-coupled receptors. 

As shown by the calculations of bacteriorhodopsin (Section 2.3.2.1), ONIOM is an excellent tool for excited-state reactions in biology. The important rhodopsin system has been studied both by TD-B3LYP Amber [80] and CASSCF Amber [81]. Another example of the combination of CASSCF with Amber for the surrounding protein can be found for the yellow protein [82],... 

Proton gradients can be built up in various ways. A very unusual type is represented by bacteriorhodopsin (1), a light-driven proton pump that various bacteria use to produce energy. As with rhodopsin in the eye, the light-sensitive component used here is covalently bound retinal (see p. 358). In photosynthesis (see p. 130), reduced plastoquinone (QH2) transports protons, as well as electrons, through the membrane (Q cycle, 2). The formation of the proton gradient by the respiratory chain is also coupled to redox processes (see p. 140). In complex III, a Q,cycle is responsible for proton translocation (not shown). In cytochrome c oxidase (complex IV, 3), trans-... 

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

Wavepacket motion is now routinely observed in systems ranging from the very simple to the very complex. In the latter category, we note that coherent vibrational motion on functionally significant time scales has been observed in the photosynthetic reaction center [15], bacteriorhodopsin [16], rhodopsin [17], and light-harvesting antenna of purple bacteria (LH1) [18-20]. Particularly striking are the results of Zadoyan et al. [21] on the... 

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. 

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