Carbohydrate-binding specificity of silkworm lectin.

The binding specificity of a lectin from the hemolymph of silkworm larvae was examined quantitatively by taking advantage of the fluorospectrophotometric properties of the lectin. On excitation at 280 nm, the lectin fraction gave a fluorescence-emission spectrum centered at 336 nm, which was attributable to tryptophan residues. The fluorescence could be completely quenched by the addition of specific saccharides. The affinity constants of the silkworm lectin with specific saccharides were calculated from the changes in intensities of fluorescence-difference spectra induced by the saccharides. The silkworm lectin had the highest affinity for dermatan sulfate and hyaluronic acid, followed by protuberic acid, heparin, and chondroitin sulfate A. Among monosaccharides tested, only D-glucuronic acid and N-acetyl-neuraminic acid induced weak but significant quenching, and their affinity constants were found to be low. These results indicate that the silkworm lectin has a strong affinity for carboxyl groups, especially alpha-L-iduronic acid residues, in the saccharides. In most cases, sulfate groups on the saccharides interfere with the specific interactions.