Properties of α-galactosidase II(2) from Vicia faba seeds

α-Galactosidase II(2) (MW ∼ 43 390) from resting Vicia faba L. seeds had been shown to possess D-glucose/D-mannose-specific lectin activity. Inhibition studies with monosaccharides and an examination of the effects of heat and pH on the catalytic and lectin activities of the enzyme indicate that the enzyme substrate and the lectin haptens bind at different sites on the protein. D-Mannosebinding has been investigated by equilibrium dialysis and spectrophotometrically. Both methods yield Ka values of approx. 3·10(3) M(-1) for the interaction and there would appear to be two mannosebinding sites per molecule of enzyme protein. The lectin properties of V. faba α-galactosidase II(2) have been discussed in relation to both V. faba lectin (favin) and other legume α-galactosidases.