Calculating Half Maximal Inhibitory Concentration (IC50) Values from Glycomics Microarray Data Using GraphPad Prism

Half maximal inhibitory concentration (IC50) is a measurement often used to compare the efficiency of various carbohydrates and their derivatives for inhibition of lectin binding to particular ligands. IC50 values can be calculated using experimental data from various platforms including enzyme-linked immunosorbent assay- (ELISA-)type microtiter plate assays, isothermal titration calorimetry (ITC), or glycan microarrays. In this chapter, we describe methods to fluorescently label a lectin, to carry out a lectin binding inhibition experiment on glycan microarrays, and to calculate the IC50 value of a binding inhibitory molecule using GraphPad Prism software. In the example used to illustrate the method in this chapter, IC50 calculation is demonstrated for inhibition of Maackia amurensis agglutinin (MAA) binding to 3′sialyl-N-acetyllactosamine (3SLN) using free lactose.