Properties of Succinylated Wheat‐Germ Agglutinin

Abstract

The physicochemical and binding properties of succinylated wheat germ agglutinin are described in comparison with these of unmodified wheat germ agglutinin. Succinylated wheat germ agglutinin is an acidic protein with a pI [isoelectric point] of 4.0 .+-. 0.2 while the native lectin is basic, pI of 8.5. The solubility of succinylated wheat germ agglutinin is about 100 times higher than that of the unmodified lectin at neutral pH. Both lectins are dimeric at pH down to 5, and the dissociation occurs at pH lower than 4.5. The binding of oligosaccharides of N-acetylglucosamine to both lectins is very similar on the basis of fluorescence and phosphorescence studies. The minimal concentration required to agglutinate rabbit red blood cells is about 2 .mu.g/ml with both lectins and the concentrations of N-acetylglucosamine and di-N-acetylchitobiose which inhibit agglutination are similar with both lectins. The number of succinylated wheat germ agglutinin molecules bound to the surface of mouse thymocytes was 10 times lower than that of the unmodified lectin although the apparent binding constant was only slightly different between the 2 lectins. The dramatic decrease of the apparent number of cell surface receptors upon succinylation of the lectin is discussed on the basis of the decrease of the pI and of the acidic properties of the cell surface.