Bacteria rhodopsin

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-... 

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. 

Indeed, some proteins we have discussed in this book have sequences or shapes similar to other proteins. For example, antibodies are shaped similarly to a protein called superoxide dismutase, which helps protect the cell against damage by oxygen. And rhodopsin, which is used in vision, is similar to a protein found in bacteria, called bacteriorhodopsin, which is involved in the... 

The role of retinal (18, vitamin A aldehyde) in the visual process, involving cis/trans isomerisation of the sterically hindered C-11,12 double bond, is well established [28,29]. Besides the important function of retinal in visual signal transduction in animals is the function of energy production in halophilic bacteria, where the retinal-based bacterio-rhodopsin takes part in a light driven proton pump [30]. 

RHODOPSIN THE SOLAR-POWERED PROTEIN YOU SHARE WITH BACTERIA... 

Rhodopsin is a solar panel for the cell. If you shine a hght on bacteria with rhodopsin, they will push protons out and acidify their surroundings. The only cost to the bacterium is the cost to make the protein (and replace it when it breaks). The energy from the sun is free. 

Your rhodopsin may look primitive, but it serves an advanced function. It detects light in the retina of your eye. As you read this, carbon chains inside rhodopsins are detecting photons by flipping back and forth and pushing a protein around, just like in a pink sample of light-sensitive bacteria. 

For both photosensor and photocoupling light quanta must be detected by specific receptor molecules. In blue-green algae and purple bacteria the same pigments, chlorophyll and bacteriochlorophyll respectively, serve as photoreceptors for photocoupling and phototaxis. Similarly bacterio-rhodopsin, the photosynthetic pigment of Halobacterium, also mediates a step-down photophobic response. Halobacterium also possesses a second... 

In bacteria, finally, the photoreceptor molecules can be embedded into the cell membrane (as is the case of sensory rhodopsins in H. salinarum, see Chapter 124) or can simply be located in the cytoplasm (as is the case of PYP in H. halophila, see Chapter 123). 

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