Four identical subunits in jack fruit seed agglutinin offer only two saccharide binding sites

Gel filtration of jack fruit seed agglutinin in 6 M guanidine hydrochloride confirmed our earlier report that the native 39.5‐kDa protein was a tetramer of identical noncovalently associated 10‐kDa subunits. Binding studies by the fluorescence quenching method using 4‐methylumbelliferyl α‐D‐galactoside as well as equilibrium dialysis using p‐nitrophenyl α‐D‐galactoside indicated only two binding sites per tetramer. This behaviour resembles the half‐of‐the‐sites reactivity in certain enzymes and is discussed in view of the small subunit size.