Detection of lectin-sugar interaction by ultraviolet difference spectroscopy.

It was found that the addition of specific sugars to solutions of several lectins induced ultraviolet difference spectra. The difference spectra of lectins from Lens culinaris, Sophora japonica, Solanum tuberosum and wheat germ have two peaks at 292 nm and 284-287 nm which are characteristic of the tryptophanyl residue. The difference spectrum of Arachis hypogaea agglutinin has two peaks at 285 nm and 279 nm which seem to be characteristic of the tyrosyl residue. In addition to the identification of these amino acid residues as being in or near the sugar binding sites of the lectins, the binding constants of these lectins with the specific sugars can be easily determined from the intensities of the difference spectra at various concentrations of sugars. This method may be useful for the simple and direct determination of the binding constants of lectins with various naturally occurring sugars which have no chromogenic groups.