Circular dichroism study of membrane dynamics focused on effect of monosialogangliosides

Monosialogangliosides (GM) purified from bovine brain were incorporated into circular dichroism (CD)-active liposomes and the effects of GM on the membrane dynamics were studied by CD spectroscopy. In the presence of 7 mol% of GM, the phase transition temperature (Tc) of the membrane increased by ca. 10 degrees C compared with the membrane without GM and characteristic CD spectra were observed for CD-active liposomes incorporating GM at low temperature. Asialogangliosides had no effect on the CD spectra or Tc. We have also studied the role of GM in reducing leakage of [3H]sucrose from liposomes composed of egg phosphatidylcholine, dipalmitoyl phosphatidic acid, cholesterol and alpha-tocopherol with a molar ratio of 4 : 1 : 5 : 0.1 in the presence of human plasma at 25 degrees C. The half-life of [3H]-sucrose leakage was 173 h for liposomes incorporating 7 mol% of GM. On the other hand, the half-lives for liposomes incorporating 7 mol% of asialogangliosides and liposomes without glycolipids were 45 and 42 h, respectively. These results indicate that sialic acid on the membrane surface contributes to the increase of Tc, to the change of the aggregation state of phospholipids and to the stabilization of liposomes in plasma.