Complexing of heparin with phosphatidylcholine. A possible supramolecular assembly of plasma heparin.
In a series of attempts to reveal plasma heparin, we found that high ionic strength and modification of protein amino groups were not effective in extracting endogenous heparin (or, indeed, a large percentage of exogenous labelled heparin), whereas delipidation in the presence of 4M-guanidinium chloride gave high yields, indicating that plasma heparin may be assembled with compounds other than proteins, in a form making it inaccessible to water and ions. During the extraction of lipids, a paradoxical entry of heparin into the organic phase was observed. Detergents, including sodium dodecyl sulphate, did not shift heparin into the aqueous phase, whereas repeated chloroform/methanol extraction did so. Using purified compounds we were able to reproduce in vitro both the scavenging of heparin from water as well as the formation of heparin-phosphatidylcholine complexes soluble in organic solvents. Evidence for complexing of heparin with phosphatidylcholine was also obtained by electrophoretic and ultracentrifugation assays. The quaternary-ammonium-containing phosphatidylcholine was the more effective phospholipid in binding heparin; anionic phospholipids did not bind. Only heparin-like glycosaminoglycans bound phosphatidylcholine, but less-sulphated compounds (heparan sulphate and dermatan sulphate) were weaker ligands. Gel-filtration experiments showed that heparin was not bound to liposome vesicles, but that a measurable percentage of the phospholipids was stripped off from vesicles and was found in the form of a complex separable from liposomes by gel filtration. The molecular basis as well as the biological role of the interaction of heparin with major membrane phospholipids are discussed.
D002725:Chloroform; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D006493:Heparin / Q000097:blood; D006801:Humans; D046911:Macromolecular Substances; D000432:Methanol; D010713:Phosphatidylcholines; D012995:Solubility; D014461:Ultracentrifugation
D046911:Macromolecular Substances; D010713:Phosphatidylcholines; D002725:Chloroform; D006493:Heparin; C028694:1-palmitoyl-2-oleoylphosphatidylcholine; D000432:Methanol