β-Galactoside-binding activity of human galectin-1 at basic pH

► β-Galactoside binding activity of human galectin-1 is evaluated at basic pH. ► Lactose binding constant Kb is constant at pH 7-9.5. ► Lactose gel-binding fraction Y may decrease depending on pH and NaCl concentration. ► Coulombic repulsion among hGal-1 causes pH and NaCl concentration dependence of Y. ► Coulombic repulsion mainly arises from deprotonation of Cys at pH 8.5 ± 0.1.