Fluorescence spectral studies on the specific interaction between sulfated glycosaminoglycans and potato lectin

On excitation at 280 nm, Solanum tuberosum agglutinin (STA) produced a fluorescence emission spectrum with a maximum at 347 nm, which is typical of tryptophanyl residues. The fluorescence emission maximum was shifted toward shorter wavelength and quenched by the addition of specific sugars. The changes were analyzed precisely and quantitatively by measuring the fluorescence difference spectra. This method required far smaller amounts of samples than UV-difference spectroscopy to obtain the binding parameters. The binding constants of chitin sulfate, keratan sulfate, and highly sulfated keratan sulfate were calculated to be 1.8 X 10(5) M-1, 3.4 X 10(5) M-1, and 5.2 X 10(5) M-1, respectively. The results indicate that consecutive and non-consecutive, alternating (1 leads to 4)-N-acetyl-beta-D-glucosaminyl residues in the glycosaminoglycans can interact freely with STA in spite of the existence of the sulfate groups at C-6 of the N-acetyl-D-glucosaminyl residues and extra sulfate groups at C-6 of the galactosyl residues linked with N-acetyl-6-O-sulfo-beta-D-glucosamine.