Binds in decreasing order of affinity: galacturonic acid, D-galactosamine, methyl-alpha-D-galactopyranoside and further galactose-containing carbohydrates. Has hemagglutinating activity against human and rabbit erythrocytes. Optimum pH is 6-7. Activity is stable up to 60 degrees Celsius, then decreases and is lost at 80 degrees Celsius. Homodimer; disulfide-linked. Contains disulfide bonds. Dimer.