Studies of the kinetics of sterol exchange between vesicles.
Item
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Title
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Studies of the kinetics of sterol exchange between vesicles.
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Identifier
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AAI9108127
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identifier
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9108127
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Creator
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Kan, Chu-Cheng.
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Contributor
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Adviser: Robert Bittman
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Date
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1990
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Biochemistry
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Abstract
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The rates of desorption of {dollar}\beta{dollar}-sitosterol (24{dollar}\alpha{dollar}-ethylcholesterol) from donor species are lower than those of cholesterol by factors of 3 to 9. It is concluded that the 24{dollar}\alpha{dollar}-ethyl group contributes to impeding spontaneous transfer of sitosterol between lipid surfaces. The half-times for cholesterol exchange from vesicles prepared with 3-methoxy- or 3-deoxy-N-C18-SPM were only slightly faster than that found using vesicles prepared from N-C18-SPM. Vesicles containing O-ethyl-N-C18-SPM and O-THP egg SPM gave rate enhancements of {dollar}\sim{dollar}14 and 35, compared with the rates observed in vesicles made from N-C18- and egg SPM, respectively. These measurements indicate that hydrogen bonding of the hydroxyl group of SPM with cholesterol does not contribute to the slow desorption of cholesterol. The half-times for cholesterol exchange from vesicles of synthetic PCs containing a sn-2 N-linked chain are not very different from that obtained using DPPC vesicles, although the exchange rate was much slower in N-C16-SPM than in DPPC vesicles. The rates of cholesterol exchange from vesicles prepared from PCs containing a sn-2 S-linked chain are also similar to the rate of cholesterol exchange from DPPC vesicles. This indicates that the interlipid hydrogen-bonding between cholesterol and PC does not play a major role in determining the rate of cholesterol desorption.;Synthetic (4- {dollar}\sp{14}{dollar}C) cholesterol analogs were used to reveal the effect of structural modifications on sterol movement. ({dollar}\sp{14}{dollar}C) Epicholesterol and ({dollar}\sp{14}{dollar}C) triethoxycholesterol undergo exchange at rates much faster than cholesterol. The movement of ({dollar}\sp{14}{dollar}C) 3-aminocholesterol and ({dollar}\sp{14}{dollar}C) cholesteryl diazoacetate is biphasic, indicating the existence of two kinetic pools of these sterol derivatives in the lipid matrix of the donor species. The slow kinetic phase may reflect the slow transbilayer migration of these charged cholesterol analogs from the inner to outer monolayer. 7-Ketocholesterol and 7-{dollar}\alpha{dollar}- or 7{dollar}\beta{dollar}-hydroxycholesterol undergo exchange much more rapidly than cholesterol, probably because of the weak lipophilic interactions between oxysterols and DPPC. ({dollar}\sp{14}{dollar}C) 5{dollar}\alpha{dollar}-Cholestan-3{dollar}\beta{dollar}-ol undergoes desorption only slightly more slowly than that does cholesterol. The effect of sterol mol % on the rate of sterol exchange was investigated. It seems that the rate of exchange is sensitive to the size of the sterol-rich domain in vesicles. (Abstract shortened with permission of author.).
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
