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Beschreibungen/Notizen
Circular dichroism measurements were carried out on poly(
l-lysine) in the presence of vesicles of the negatively charged phospholipids, phosphatidylserine (PS; from bovine brain), phosphatidic acid (PA; prepared from egg yolk lecithin) and dimyristoylphosphatidylglycerol (DMPG). PS vesicles induced a conformational change in poly(
l-lysine) from random coil to α-helix structure in 5 mM Tes (pH 7.0), whereas PA vesicles gave rise to β-structure in the same buffer. The fraction of α-helix,
F
α (or β-structure,
F
β), increased with increasing PS (or PA) concentration, reaching a saturation value of about 0.7 (or about 1). Mixed vesicles comprising PS and dilauroylphosphatidylcholine (DLPC) also induced α-helix conformation, however, the saturation value of
Fα diminished with decreasing PS content in mixed vesicles. On the other hand, the spectral patterns for poly(
l-lysine) in DMPG vesicle suspensions exhibited the coexistence of α-helix and β-structure. Both
F
α and
F
β increased with DMPG concentration and reached saturation values of about 0.5. Mixed vesicles composed of DMPG and dimyristoylphosphatidylcholine (DMPC) led to a reduction in
F
β, while
F
α remained almost constant. The diversity in ordered structure induced by different phospholipid vesicles suggests the participation of lipid head groups in determining the secondary structure Of poly(
l-lysine) adsorbed on the vesicular surface.