Bacteriorhodopsin membrane

Ethanol and choline glycerolipids were isolated from calf brain and beef heart lipids by PTLC using silica gel H plates. Pure ethanol amine and choline plasmalogens were obtained with a yield of 80% [74]. Four phosphohpid components in the purple membrane (Bacteriorhodopsin) of Halobacterium halobium were isolated and identified by PTLC. Separated phosphohpids were add-hydrolyzed and further analyzed by GC. Silica gel G pates were used to fractionate alkylglycerol according to the number of carbon atoms in the aliphatic moiety [24]. Sterol esters, wax esters, free sterols, and polar lipids in dogskin hpids were separated by PTLC. The fatty acid composition of each group was determined by GC. 

Bromley, KM., Patil, A.J., Seddon, A. M., Booth, P. and Mann, S. (2007) Bio-functional mesolamellar nanocomposite based on inorganic/ polymer intercalation in purple membrane (Bacteriorhodopsin) films. Advanced Materials, 19, 2433—2438. 

Purple membrane(PM) of the extreme halophile Halobacterium halobium is another efficient photosynthetic system.Upon the absorption of visible light the unique protein of this membrane,bacteriorhodopsin (BR),undergoes a complicated photocycle and extrudes protons from the cell interior against their concentration gradient across the membrane.The free energy associated with this electrochemical gradient is used to transform ADP into ATP in the final step of photosynthesis (1,2). 

Halobacterium halobium purple membrane/bacteriorhodopsin Mitochondrial Fi-ATPase... 

TaUent, J., Song, Q.W, Li, Z., Stuart, J., and Birge, RR, Effective photochromic nonlinearity of dried blue-membrane bacteriorhodopsin films. Optics Lett., 21, 1339-1341,1996. 

Olle Edholm, Oliver Berger, and Fritz Jahnig. Structure and fluctuations of bacteriorhodopsin in the purple membrane. J. Mol. Biol., 250 94 111, 1995. 

Protein Computers. The membrane protein bacteriorhodopsin holds great promise as a memory component in future computers. This protein has the property of adopting different states in response to varying optical wavelengths. Its transition rates are very rapid. Bacteriorhodopsin could be used both in the processor and storage, making a computer smaller, faster, and more economical than semiconductor devices (34). 

A continuous lipidic cubic phase is obtained by mixing a long-chain lipid such as monoolein with a small amount of water. The result is a highly viscous state where the lipids are packed in curved continuous bilayers extending in three dimensions and which are interpenetrated by communicating aqueous channels. Crystallization of incorporated proteins starts inside the lipid phase and growth is achieved by lateral diffusion of the protein molecules to the nucleation sites. This system has recently been used to obtain three-dimensional crystals 20 x 20 x 8 pm in size of the membrane protein bacteriorhodopsin, which diffracted to 2 A resolution using a microfocus beam at the European Synchrotron Radiation Facility. 

Gram-negative bacteria are surrounded by two membranes, an inner plasma membrane and an outer membrane. These are separated by a periplasmic space. Most plasma membrane proteins contain long, continuous sequences of about 20 hydrophobic residues that are typical of transmembrane a helices such as those found in bacteriorhodopsin. In contrast, most outer membrane proteins do not show such sequence patterns. 

In contrast to bacteriorhodopsin or the reaction center, there is no direct contact within the membrane between the a helices in this complex. The helices are held together through contacts mediated by the pigments and by contacts at the ends of the polypeptide chains outside the membrane. 

ITowever, membrane proteins can also be distributed in nonrandom ways across the surface of a membrane. This can occur for several reasons. Some proteins must interact intimately with certain other proteins, forming multisubunit complexes that perform specific functions in the membrane. A few integral membrane proteins are known to self-associate in the membrane, forming large multimeric clusters. Bacteriorhodopsin, a light-driven proton pump protein, forms such clusters, known as purple patches, in the membranes of Halobacterium halobium (Eigure 9.9). The bacteriorhodopsin protein in these purple patches forms highly ordered, two-dimensional crystals. 

The purple patches of the Halobaeterium halobium membrane, which contain the protein bacteriorhodopsin, are approximately 75% protein and 25% lipid. If the protein molecular weight is 26,000 and an average phospholipid has a molecular weight of 800, calculate the phospholipid to protein mole ratio. 

It is interesting to compare the thermal-treatment effect on the secondary structure of two proteins, namely, bacteriorhodopsin (BR) and photosynthetic reaction centers from Rhodopseudomonas viridis (RC). The investigation was done for three types of samples for each object-solution, LB film, and self-assembled film. Both proteins are membrane ones and are objects of numerous studies, for they play a key role in photosynthesis, providing a light-induced charge transfer through membranes—electrons in the case of RC and protons in the case of BR. 

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