Membranes archaebacterial

Ether-linked lipids constitute up to 35% of the total phospholipid in molluscs. Although they are usually regarded as animal constituents, small amounts of ether-linked lipids have been identified in plants. The major phospholipids of archaebacterial membranes are ether-linked derivatives of the polyprenyl phytanyl group and of the dimeric biphytanyl group (Chapter... 

Thompson et al. have developed a few symmetric, tetraether bolaamphiphiles 19a, 19b, with anionic headgroups [48]. The aqueous dispersions of these lipids behave as good mimics of archaebacterial membranes. 

Because of the stability problems with conventional liposomes, scientists have sought many methods to stabilize them. One important development is the sterically stabilized liposomes (SSLs), which are sometimes called stealth liposomes. 25-28 Synthetic polymers are used for steric stabilization. Another approach involves cross-linking membrane components covalently or by the polymerization of polymerizable lipids.29,30 A third approach utilizes unusually stable archaebacterial membrane lipids mimics.31... 

Zang, D.L., Daliels, L., and Poulter, C.D. (1990) Biosynthesis of archaebacterial membranes formation of isoprene ethers by a prenyl transfer reaction./. Am. Chem. Soc., 112,1264—1265. 

The stereochemistry of phosphoglycerides was discussed in Chapter 1. The phosphoglycerides are a very widespread and diverse group of structures. In most membranes they are the main lipid components and, indeed, the only general exceptions to this statement are the photosynthetic membranes of plants, algae and cyanobacteria and the archaebacterial membranes. 

Halocyanin and sulfocyanin are archaebacterial cupre-doxins that are attached to peripheral membranes through a lipid anchor at their N-terminus. Halocyanin was the first cupredoxin purified from an archaeon, haloalkaliphilic Natronobacterium pharaonis These cells live in high pH (around 10-11) and in extreme salinity (30%) environments. The presence of the blue copper protein, sulfocyanin in Sul-folobus acidocaldarius was first predicted from its gene sequence. It has been subsequently purified as a recombinant protein and shown to bind a single copper ion with spectroscopic properties typical for a blue copper site. ... 

The archaebacterial lipids have been used to prepare liposomes. They form monolayer lipid membranes70 rather than the normal bilayer type because there are polar groups on both ends of the a,oo-dicarboxylic acids. Membrane lipids extracted from these bacteria have also been used to form liposomes. Physical studies showed positive results such as extra stability at high temperature, at high or low pH, and in other harsh conditions.71-74... 

Fig. 1.4 (a) Generalized membrane structure. Hydrophobic heads of amphipathic molecules are shown in black and hydrophilic tails as wavy lines. Membrane reinforcers are shown as boxes and can be likened to nails spanning half the membrane (e.g.sterols and hopanoids) or rivets spanning the entire membrane (e.g. carotenoids). Where they are absent, in archaebacterial thermophiles, the amphipathic molecules span the entire membrane and act as struts , (b) Possible steps in the self-assembly of primitive membranes (M2+ are metal ions). 

Fig. 2.15 (a) Examples oflipids in the membranes and cell walls of eubacteria. (b) Phytanyl ether lipids in archaebacterial cell membranes. 

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