Specific binding of concanavalin A to free inositol and liposomes containing phosphatidylinositol.
We previously reported that concanavalin A could bind specifically to liposomes containing phospholipids and lacking glycoconjugates (Biochem. Biophys. Res. Comm. 74, 208, 1977). In the present study we show that the binding of concanavalin A to the liposomes was greatly increased (up to 5 fold) by the presence of phosphatidylinositol in the liposomes. Furthermore, the binding of concanavalin A to phosphatidylinositol-liposomes was specific and could be inhibited by either alpha-methyl mannoside or by myo-inositol. We also found that concanavalin A-induced lymphocyte mitogenesis could be inhibited either by alpha-methyl mannoside or by myo-inositol. Simultaneous addition of both inhibitors to concanavalin A and liposomes showed that inhibition was non-competitive: alpha-methyl mannoside was more inhibitory to liposomes lacking phosphatidylinositol, and myo-inositol was more inhibitory to liposomes containing phosphatidylinositol. This suggests that the binding site for inositol might be different than that for mannose. Equilibrium dialysis and Scatchard plots revealed 4 binding sites each for inositol and mannose at neutral pH. The binding constants of concanavalin A were 0.13 X 10(4) and 0.25 X 10(4) liters/mole respectively for inositol and mannose. We conclude that concanavalin A binds specifically to the inositol portion of phosphatidylinositol.
D000818:Animals; D001667:Binding, Competitive; D003208:Concanavalin A / Q000378:metabolism*; D007294:Inositol / Q000378:metabolism*; D008081:Liposomes; D008213:Lymphocyte Activation; D008214:Lymphocytes / Q000276:immunology; D008766:Methylmannosides / Q000378:metabolism; D051379:Mice; D010716:Phosphatidylinositols / Q000378:metabolism*
D008081:Liposomes; D008766:Methylmannosides; D010716:Phosphatidylinositols; D003208:Concanavalin A; D007294:Inositol; C008466:methylmannoside