ABSTRACT
On binding to Vicia faba lectin, the fluorescence of 4-methylumbelliferyl-α-Dglucopyranoside was quantitatively quenched showing that the interaction of 4- methylumbelliferyl-α-D-glucopyranoside took place in a binding environment. The binding of the fluorescent sugar was saccharide specific as evidenced by the reversal of 4-methylumbelliferyl- α-D-glucopyranoside fluorescence quenching by D-fructose. The association constant, Ka, values for the 4-methylumbelliferyl-α-D-glucopyranoside was determined by competition study employing reversal of fluorescence quenching of 4-methylumbelliferyl-α- D-glucopyranoside by D-fructose. The Ka value obtained for D-fructose was 1·07 ± 0·03 × 104 M–1 and for 4-methylumbelliferyl-α-D-glucopyranoside was 1·60 ± 0·05 × 104 M–1 at 15°C. The Ka values of 2·51 ± 0·06 × 104 M–1, l·26 ± 0·02 × 104 Μ–1 and 0·56 ± 0·01 × 104 M–1, respectively at 10°, 20° and 30°C were obtained from the Chipman equation. The relative fluorescence quenching, Δ Fa, at infinite concentration of the free saccharide sites of Vicia faba lectin [P’] was 93·5% at 30°C and the binding constant for 4-methylumbelliferyl-α-Dglucopyranoside lectin interaction as derived by Yank and Hanaguchi equation was 0·63 ± 0·01 × 104 M–1.