Lipid bilayer stability in membranes. Regulation of lipid composition in XXXX as governed by molecular shape.

@entity844 @entity43897 @entity39045 @entity43898 @entity7294 @entity1718 @entity165
The polar lipid composition in membranes of @entity39045 is extensively regulated as a response to environmental changes. In particular, the ratio between the dominating lipids @entity43897 and @entity43898 is altered depending on temperature, configuration of incorporated @entity1718 , and membrane @entity165 content. Synthesis of @entity43897 is stimulated by low temperature and @entity1718 but diminished by the presence of @entity165 . These factors are likely to affect the molecular geometry of the membrane lipids. @entity43897 and @entity43898 have wedge- and rodlike molecular shapes, respectively, that are modifiable to a certain extent. The packing constraints of lipids in amphilphilic aggregates, i.e., @entity7294 -water interfacial area, @entity7294 chain volume, and @entity7294 chain length, are very important in determining the aggregate structure [Israelachvili, J. N. Mitchell, D. J., _ Ninham, B. W. (1976) J. Chem. Soc., Faraday Trans. 272, 1525]. Pure @entity43897 forms a reversed hexagonal (HII) phase structure with different @entity844 contents, while @entity43898 forms a lamellar phase. However, the only lipid structure compatible with a functional biological membrane is the lamellar phase. Consequently, the balance between lipids forming lamellar and other mesophase structures must keep within certain limits. Here we show that the response in A. liaidlawii lipid metabolism following external and internal stimuli can be predicted on the basis of molecular shapes and is necessary for the cell in order to maintain optimal membrane stability. Furthermore, the reduced capacity of @entity39045 membranes to incorporate @entity165 is another consequence of this regulation, aiming at preservation of bilayer stability.
