Further chemical modification studies on concanavalin A, the carbohydrate binding protein of the jack bean

Abstract

Acetylation of concanavalin A with N-acetyl imidazole (30 molar excess of N-acetyl imidazole) demonstrated that "accessible" tyrosyl residues must not be directly involved in the binding of carbohydrates. More extensive modification with this reagent led to inactivation of the protein. Attempted affinity labelling of the concanavalin A binding sites with a series of p-diazophenyl glycosides failed. Treatment of concanavalin A with N-bromosuccinimide and 2-nitrophenyl sulfenyl chloride produced concomitant loss of activity with modification of tryptophanyl residues. On the other hand, it was demonstrated that several residues of tryptophan could be modified by treatment with 2-hydroxy-5-nitrobenzyl bromide without any loss in protein activity. Modification with bromoacetate and 2,3-butanedione led to inactivation of concanavalin A which appeared to be due to a general disruption of the protein structure rather than modification of specific aminoacyl residues in the carbohydrate combining sites.