JBC, Vol. 252, Issue 4, 1243-1249, Feb, 1977
Nature of interaction of dextran sulfate with lecithin dispersions and lysolecithin micelles
Y. C. Kim and T. Nishida
Lecithin and lecithin/cholesterol dispersions as well as lysolecithin
micelles were used to provide basic information on the mechanism of the
interaction of zwitterionic phospholipids with dextran sulfate. The
addition of dextran sulfate to lecithin dispersions or lysolecithin
micelles in the presence of Ca2+ produced insoluble complexes. At each Ca2+
concentration, the amount of insoluble complex formed was maximal at the
equivalence dextran sulfate/phospholipid weight ratio. An increase in CaCl2
concentration up to 10 mM progressively increased the equivalence ratios
for the phospholipids. Further increase in Ca2+ concentration did not
influence the equivalence ratio for maximal complex formation. The
conversion of lecithin dispersions into insoluble complexes was very
effective even at low Ca2+ concentrations. Approximately 70% of the
lecithin was converted to the insoluble complex at CaCl2 concentrations as
low as 0.5 mM and the complete conversion was observed at CaCl2
concentrations above 2.5 mM. In the presence of cholesterol, the
precipitation curve for insoluble complex formation became broader than
that of lecithin alone, indicating the enhancing effect of cholesterol on
the insoluble complex formation both below and above the equivalence ratio.
The stoichiometry of the interaction of the zwitterionic phospholipids with
dextran sulfate inthe presence of calcium was determined using lysolecithin
micelles. At the CaCl2 concentrations above 20 mM, the insoluble complex
possessed a ratio of lysolecithin/calcium/sulfate group of approximately
2/1/3 (mol/mol/mol). It appears that the formation of the insoluble complex
of lecithin or lysolecithin with dextran sulfate represents the mutually
enhancing interactions involving both positive and negative charges of the
zwitterionic phospholipids. These are the direct electro static interaction
between the phospholipid choline nitrogen and the sulfate groups of dextran
sulfate and the calcium cross-linking of the phosphate groups to the
sulfate groups or to the phosphate groups of neighboring phospholipids.
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