Halobacterium halobium, membrane

Fig. 1. Energy transduction in Halobacterium halobium. Membrane-linked energy transducers are...

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. 

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. 

Henderson, R., The purple membrane from Halobacterium halobium, Ann. Rev. Biophys. Bioeng., 6, 87 (1977). 

Kakinuma, K. Yamagishi, M. Fujimoto, Y. Ikckawa, N. Oshima, T. (1988) Stereochemistry of the biosynthesis of sn-2,3-0-diphytanyl glycerol, membrane lipid of Archaebacteria Halobacterium halobium. J. Am. Chem. Soc., 110,4861-3. 

Fig. 5.4. Structure of the bacteriorhodopsin from Halobacterium halobium. Ribbon diagram of bacteriorhodopsin and retinal as a ball-and-stick model. Bacteriorhodopsin crosses the membrane with seven a-helices that are arranged in a bundle form with the chromophore retinal bound in the interior. According to Kimura et al. (1997), with per-...

In this laboratory we have examined the ORD of various membrane systems including heavy beef heart submitochondrial vesicles, rat liver submitochondrial vesicles, erythrocyte ghosts, and the membranes of Micrococcus lysodeikticus, Halobacterium halobium, Halobacterium cuti-rubrum, and Mycoplasma laidlawii. The optical behavior of all these materials is strikingly similar the Cotton effects are similar to those produced by an a-helix but are red shifted to abnormally high wavelengths (71). Cotton effects arising from amide transitions in other... 

A three-dimensional structure also has been elucidated for bacteriorhodopsin, an integral membrane protein of the halophilic (salt-loving) bacterium Halobacterium halobium. This protein has been studied intensively because of its remarkable activity as a light-driven proton pump (see chapter 14). It forms well-ordered arrays in two-dimensional sheets that can be studied by electron diffraction. Measurements of the diffraction patterns show clearly that bacteriorhodopsin has seven transmembrane helices (fig. 17.12). 

A model for the structure of bacteriorhodopsin, a membrane protein from Halobacterium halobium. The protein has seven membrane-spanning segments connected by shorter stretches of hydrophilic amino acid residues. 

Ordered arrangements of proteins in membranes in vivo With the exception of the purple membrane produced by Halobacterium halobium, the order discussed in this section does not involve an exact regular geometrical structure. However, membrane bound enzymes and structure proteins associated with membranes are arranged in ways which are clearly defined and which involve definite and regular interactions between different kinds of molecule. Only thus can they carry out... 

The CD properties of SR-I, the retinal-linked phototaxis receptor of Halobacterium halobium, have been investigated [215], In contrast to bR and hR, no evidence of exciton coupling was found, which suggests that the chromophores are present in native membranes as monomers or that the interactions between chromophores are weak due to inter-chromophore distances and orientations. 

So far, no protein has been found as a common constituent of all membranes (compare the almost universal existence of the lipids PC and PE), even from the same species. Thus, it seems unlikely that there is a universal structural protein in membranes. The numbers of different proteins in a membrane vary widely according to membrane type. The plasma membrane of the bacterium Halobacterium halobium contains only 1 protein (bacteriorhodopsin), whereas the membrane of another bacterium, Escherichia coli, contains about 100. The plasma membrane of the human red blood cell contains at least 17 different proteins. 

Bacteriorhodopsin, is a retinal-containing protein in the purple membrane of a halophilic, (salt-loving) archaebacterium, Halobacterium halobium, which pumps protons out of the cell on activation by light.The three-dimensional structure of bacteriorhodopsin resembles that of rhodopsin in the eye. 

Bacteriorhodopsin, a light-driven proton pump, is a large (27000 Dalton) membrane protein, located in the purple membrane of halobacterium halobium (for a recent review see Lanyi, 1993). It spans the membrane by seven-a-helices (see Fig 6.6-7). The chro-mophore retinal is embedded inside the protein, shielded by the helices. Retinal connects to the Lys 216 of the protein via a protonated Schiff s base (Fig. 6.6-7). 

This approach has been extended by Rupley et al. (1988) to study of the water-induced percolation in hydrated purple membrane fragments of Halobacterium halobium. The results and conclusions are qualitatively similar to those reported above for lysozyme. (1) The percolation is two-dimensional, judged by the value of the critical exponent (Fig. 15). (2) Certain regions of the surface provide preferred protonic conduction paths. (3) There is a correspondence between the onset of function—here, the photoresponse—and the establishment of long-range connectivity within the surface water clusters. 

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