Bimodal solubilization of phospholipid-cholesterol vesicles in 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) solutions. Formation of filamentous and helical microstructures depends on negatively charged lipids |
| |
Authors: | T Schröder T Schürholz |
| |
Institution: | (1) Department of Biophysical Chemistry, University of Bielefeld, D-33615 Bielefeld, Germany (Fax: +49-521 106 6146), DE |
| |
Abstract: | Phospholipid/cholesterol vesicles were solu-bilized by 3-(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS).
Above 30 mol% cholesterol (Ch) in the lipid vesicles several remarkable changes of the solubilization process were observed.
(i) Two modes of solubilization: The effective detergent to lipid ratio Rc(M) for the formation of mixed micelles decreased from Rc(M) = 43 ± 3 at low lipid concentrations, L]≤ 0.15 mm, to Rc(M) = 2.4 ± 0.3 above L] = 0.5 mm (40 mol% Ch, T = 20 °C). (ii) At subsolubilizing CHAPS concentrations, filamentous and helical microstructures were formed,
similar to those which were observed in native and model bile. (iii) The number of observed fibers was about two orders of
magnitude higher in the presence of the negatively charged lipids phosphatidylglycerol (PG) and phosphatidic acid (PA) compared
to the zwitterionic phosphatidylcholine (PC). Fiber formation began after 16–18 h using PG and PA compared to 3–4 days in
the presence of PC. Screening of the charged lipids by NaCl effectively reduced the formation of fibers. Assuming binding
of Na+ to the charged lipid aggregates, an intrinsic binding constant Kint = 0.6 M–1 was determined by applying the Gouy-Chapman theory. After the addition of CHAPS to PG/Ch vesicles, a fast initial solubilization
of the vesicles (<1 min) to mixed micelles (rh = 2.3 ± 0.2 nm) and small vesicles (rh = 23 ± 1 nm) was observed, followed by an intermediate period of 2 h, after which the formation of fibers occurred (>15 h).
The microstructures are visualized by darkfield and electron microscopy. The method of vesicle solubilization is compared
to the dilution of concentrated micellar solutions, which is usually applied to model bile systems.
Received: 28 May 1996 / Accepted: 26 July 1996 |
| |
Keywords: | Gallstone Cholesterol monohydrate crystals Phase separation Light scattering Electron microscopy |
本文献已被 SpringerLink 等数据库收录! |
|