Abstract：
:Sonication of lysophosphatidylcholine (lysoPC; 20 mumol/mL) and cholesterol (chol) in aqueous medium produces lamellar structures over a wide range of concentrations. From 25 to 47 mol % cholesterol, electron microscopy (EM) after negative staining showed extended stacklike lamellae about 40 A thick. From 50 to 60 mol % chol, freeze-fracture EM showed homogeneous populations of small unilamellar vesicles averaging 260-310 A in diameter. Phosphorus-31 nuclear magnetic resonance was used to characterize the stacklike lamellae and to measure the distribution of the lysophospholipid between the outer and inner leaflet of the vesicles as a function of sterol concentration. We found that in lysoPC/chol dispersions containing less than equimolar amounts of cholesterol (25-47 mol %), the entire phosphorus signal (40.5 ppm) was shifted downfield by 10.5 ppm upon addition of Pr3+ (2.4 mM), consistent with the stacklike lamellar structures in which all lysoPC head groups are accessible to the ions. By contrast, addition of Pr3+ to lysoPC/chol vesicles containing equimolar or higher amounts of cholesterol (up to 60 mol %) gave rise to two phosphorus peaks. The more intense downfield signal (51.0 ppm) responsive to paramagnetic ions was assigned to lysoPC located in the outer vesicle leaflet. The upfield signal (40.5 ppm), which was not affected by the ions, was assigned to inside lysoPC. For lysoPC/chol (1:1) vesicles, an outside to inside lysophospholipid ratio (Ro/i) of 6.5 was determined. Essentially the same Ro/i value (6.7) was obtained on lysoPC/chol (1:1) vesicles which after dialysis contained only entrapped Pr3+.(ABSTRACT TRUNCATED AT 250 WORDS)
journal_name
Biochemistryjournal_title
Biochemistryauthors
Kumar VV,Anderson WH,Thompson EW,Malewicz B,Baumann WJdoi
10.1021/bi00401a059subject
Has Abstractpub_date
1988-01-12 00:00:00pages
393-8issue
1eissn
0006-2960issn
1520-4995journal_volume
27pub_type
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