CHEMICAL MODIFICATION AND SUGAR BINDING-PROPERTIES OF 2 MAJOR LECTINS FROM PINHAO (ARAUCARIA-BRASILIENSIS) SEEDS

Araucaria brasiliensis lectins, lectin I and lectin II, were subjected to various chemical modifications to detect the amino acid residues present in their carbohydrate binding sites. Modification of tyrosine and arginine residues did not affect binding activities of lectins. However, modification of tryptophan and histidine led to a complete loss. Modification of amino and carboxyl groups of both lectins also abolished completely their hemagglutinating capacity. The carbohydrate moiety of lectins was not involved in maintaining their hemagglutinating activities. Binding of monosaccharides was studied by UV difference spectroscopy which showed that both lectins have two binding sites with different affinities for sugars. Each lectin molecule may bind from 6 to 14 sugar residues. The association constants and free energy of binding for different sugars are presented.