Specific Binding of Concanavalin A to Free Inositol and Liposomes Containing Phosphatidylinositol

摘要

It has been previously reported that concanavalin A could bind specifically to liposomes containing phospholipids and lacking glyconjugates (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 ginding of concanavilin A to either alpha-methyl mannoside or by myo-inositol. We also found that concanavalin A-induced lypmhocyte mitogenesis could be inhibited either by alpha-methyl mannoside or by myo-insitol, Simultaneous addition both inhibitors to concanavalin and loposomes showed that inhibition was non-competitive: alpha-mehtal mannoside was more inhibitory to liposomes lacking phosphatidylinositol, and myoinositol was more inhibitory containing phosatidylinositol. This suggests that the binding site for inositol might be different than that for mannose. Equillibrium dialysis and scatchard plots revealed 4 binding sites each for inositol and mannose at neutral pH. The binding constants of concanavalin A were 1,300 and 2,500 liters/mole respectively for inositol and mannose. We conclude that concanavalin A binds specifically to the inositol portion of phosphatidylinositol.