Mixed monolayer studies of the interactions of synthetic phosphatidylcholines containing branched fatty acids and a hopane glycolipid isolated from the thermo-acidophilic bacterium bacillus acidocaldarius
✍ Scribed by Elmar Kannenberg; Alfred Blume; Ronald N. McElhaney; Karl Poralla
- Publisher
- Elsevier Science
- Year
- 1986
- Tongue
- English
- Weight
- 424 KB
- Volume
- 39
- Category
- Article
- ISSN
- 0009-3084
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✦ Synopsis
Hopanoids, a group of pentacyclic triterpenoids, are widely distributed in eubacterial membranes. In the eubacterium Bacillus acidocaldarius a hopane glycolipid, 1-(O-t3-N-acylglucosaminyt)-2,3,4-tetrahydroxypentane-29-hopane, occurs together with phospholipids containing methyl iso-and anteiso-branched fatty acids besides to-cyclohexane fatty acids. Therefore mixed monolayers of hopane glycolipid (HGL) with 1,2-diisoheptadecanoylphosphatidylcholine (DIHPC) and 1,2-dianteisoheptadecanoyl-phosphatidylcholine (DAHPC) were studied. The presence of increasing amounts of HGL in DIHPC films lowers the phase transition midpoint of the liquid-condensed/liquid-expanded transition and at 50 mol% abolishes this transition. In the liquid-expanded state of the DIHPC film, the presence of HGL results in a marked reduction in the mean molecular area occupied by the PC molecules (the condensing effect). The maximum condensation is observed at around 10 mol% HGL while higher concentrations of HGL show no further reduction in the area occupied by the phosphatidylcholine (PC). In the liquid-condensed state of the DIHPC film HGL mixes almost ideally with the PC and no condensation is observed. In liquid-expanded films of DAHPC, HGL also reduces the mean molecular areas of the PC molecules but the magnitude of this reduction increases continually with increasing HGL concentrations. At temperatures where the pure DAHPC film is in the range of the phase transition, HGL condenses the film with molecular area reductions increasing continuously with increasing HGL concentrations. The effects of HGL in liquidexpanded DIHPC monolayers are somewhat smaller than the condensations observed in the presence of cholesterol, while the condensations in DAHPC films almost equals that caused by cholesterol. These results confirm further the cholesterol like role of hopanoids in prokaryotic membranes.