Halobacterium halobium

Animals cannot synthesize vitamin A-active compounds and necessary quantities are obtained by ingestion of vitamin A or by consumption of appropriate provitamin A compounds such as P-carotene. Carotenoids are manufactured exclusively by plants and photosynthetic bacteria. Until the discovery of vitamin A in the purple bacterium Halobacterium halobium in the 1970s, vitamin A was thought to be confined to only the animal kingdom (56). Table 4 Hsts RDA and U.S. RDA for vitamin A (67). 

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. 

FIGURE 10.20 A schematic drawing of Halobacterium halobium. The purple patches ( tain bacteriorhodopsin (bR). 

Even entrapment of entire cells within reversed micelles without loss of their functionality has been achieved. For example, mitochondria and bacteria (Actinobacter cal-coaceticus, Escherichia coli, Corynebacterium equi) have been successfully solubilized in a microemulsion consisting of isopropyl pahnitate, polyoxyethylene sorbitan trioleate [162], Enhanced hydrogen photoproduction by the bacterium Rhodopseudomonas sphaeroides or by the coupled system Halobacterium halobium and chloroplasts organelles entrapped inside the aqueous core of reversed micelles with respect to the same cells suspended in normal aqueous medium has been reported [183,184],... 

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-...

Figure 3.2 Replacement of high salt with organic solvents-stability of the extracellular protease from Halobacterium halobium in 0.36 M NaCl in water or various organic solvents. The KSC value represents the Sechenow constant multiplied by the concentration of the solvent, which provides a measure of the salting-out (kosmotropic) capacity of the solution [10].

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... 

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