An efficient method for the synthesis and purification of N-[3-(3-[125I]iodo-4-hydroxybenzyl)propionyl]-phosphatidylethanolamine (125I-phenylpropionyl-PE), a non-exchangeable iodinated lipid of high specific radioactivity, is described. The technique involves acylation of phosphatidylethanolamine with N-succinimidyl 3-(3-[125I]iodo-4-hydroxyphenyl)propionate (monoiodinated Bolton-Hunter reagent) and purification by thin-layer chromatography. Quantitative incorporation of the iodinated lipid into vesicles prepared by a variety of techniques was observed to occur. With these vesicles, no transfer of the labeled lipid to other vesicles or cells occurred, irrespective of vesicle composition or the presence of other transferable lipids in the same bilayer membranes. This, 125I-phenylpropionyl-PE appears to be an accurate liposome tracer and can be used in a variety of in vitro and in vivo assays that require high levels of sensitivity unobtainable with most other lipid-labeling techniques.
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