Interaction of concanavalin A with spin-labeled glycolipid incorporated into liposomes

Using a synthetic glycolipid derived from maltotetraose and a spin-labeled fatty acid, the lateral distribution and molecular motion of the spin-labeled glycolipid on phosphatidylcholine liposomes in the presence and absence of concanavalin A were examined. When the spin-labeled glycolipid was added to preformed egg yolk phosphatidylcholine-dicetyl phosphate (molar ratio, 10 : 1) liposomes, most of the spin-labeled glycolipid molecules could be incorporated into liposomes as shown by their concanavalin A-induced agglutination. Concanavalin A also caused a change in line width of the ESR signal of liposome-bound spin-labeled glycolipid, whereas the overall splitting value 2A parallel did not change significantly. It is suggested that the binding of glycolipid molecules to concanavalin A increased the interactions among the radicals of the probe but that the mobility of the acyl chain off glycolipids was not affected. These signal changes were also observed with succinyl-concanavalin A. However, in contrast to concanavalin A, no appreciable agglutination of liposomes could be induced by the latter concanavalin A derivative. Both the agglutination of liposomes and the change in line width of the ESR signal were completely inhibited by alpha-methyl-D-mannoside.