Interaction between polySia-NCAM and DA measured by frontal affinity chromatography. Elution profiles of DA after application to a column of immobilized STX(WT)-derived polySia-NCAM (A), STX(G421A)-derived polySia-NCAM (B), and STX(C621G)-derived polySia-NCAM (C). DA was dissolved in PBS at concentrations of 10 μm (blue), 20 μm (pink), and 30 μm (yellow), and 2 ml of each solution was applied to the column (126 μl) through a 2-ml loop at a flow rate of 0.125 ml/min at 25 °C. Each elution pattern is superimposed on that of acetylcholine (black). The Kd values of STX(WT)- and STX(C621G)-derived polySia-NCAM were 8.6 and 19 μm, respectively. The Kd value of STX(G421A)-derived polySia-NCAM could not be calculated.