Determination of the affinity constants of pea lectin for neutral sugars by capillary affinophoresis with a monoligand affinophore.

Affinophoresis is a type of affinity electrophoresis in which an affinophore, a conjugate of an affinity ligand and a multiply charged soluble matrix, causes a change in migration velocity of proteins which have a specific affinity for the ligand. A monoligand affinophore bearing a mannoside was prepared by coupling iodoacetylated p-aminophenyl alpha-D-mannoside to the free thiol group of N-succinylated glutathione, and used for the affinophoresis of pea lectin in a capillary. The electrophoretic mobility of pea lectin towards the anode increased in the presence of the affinophore as a function of its concentration in a manner that is described by the equation for affinity electrophoresis. Analysis of the suppression of the affinophoresis on the addition of neutral sugars to the system allowed the determination of the dissociation constants of the lectin for these neutral sugars. The dissociation constants obtained on affinophoresis agreed well with the values in the literature. The preparation of a monoligand affinophore for ligands bearing an amino group should facilitate the application of this type of microscale analysis (0.14 ng of protein for each run) to protein ligand interactions.