Ultraviolet difference spectroscopy study of peanut lectin binding to Mono- and disaccharides

Ultraviolet difference spectroscopy was used to study the interaction of peanut (Arachis hypogaea) lectin with complementary carbohydrates. A correlation was observed between variations of ultraviolet spectra during the binding of sugars to the lectin and the specificity and the strength of the binding. The association constant, free energy, enthalpy and entropy for peanut lectin-lactose interactions were calculated over the temperature range 10-30 degrees C. The binding constants for 10 mono- and disaccharides containing a D-galactopyranosyl or a D-talopyranosyl residue were calculated. Comparing their effectiveness to interact with peanut lectin, methyl alpha-D-galactopyranoside appeared to have a more marked affinity than lactose; D-galacturonic acid and methyl 7-deoxy-D-glycero-beta-D-galacto-heptopyranoside had no measurable affinity; the other sugars showed a lower affinity than lactose. The correlations between these differences and the conformations of the sugars obtained by X-ray analysis are discussed.