Studies on tryptophan residues of Abrus agglutinin. Stopped-flow kinetics of modification and fluorescence-quenching studies.
The presence of two essential tryptophan residues/molecule was implicated in the binding site of Abrus agglutinin [Patanjali, Swamy, Anantharam, Khan & Surolia (1984) Biochem. J. 217, 773-781]. A detailed study of the stopped-flow kinetics of the oxidation of tryptophan residues revealed three classes of tryptophan residues in the native protein. A discrete reorganization of tryptophan residues revealed three classes of tryptophan residues in the native protein. A discrete reorganization of tryptophan residues into two phases was observed upon ligand binding. The heterogeneity of tryptophan exposure was substantiated by quenching studies with acrylamide, succinimide and Cs+. Our study revealed the microenvironment of tryptophan residues to be hydrophobic, and also the presence of acidic amino acid residues in the vicinity of surface-localized tryptophan residues.
D000178:Acrylamides; D001666:Binding Sites, Antibody; D001974:Bromosuccinimide; D002586:Cesium; D007700:Kinetics; D007785:Lactose; D037102:Lectins; D010084:Oxidation-Reduction; D013050:Spectrometry, Fluorescence; D013388:Succinimides; D014364:Tryptophan / Q000032:analysis*
D000178:Acrylamides; D037102:Lectins; D013388:Succinimides; D002586:Cesium; D014364:Tryptophan; D007785:Lactose; D001974:Bromosuccinimide