title: Interaction of radical anion probes with glucoamylase I from Aspergillus niger.
abstract: The radical anions (SCN)2.- and Br2.- produced during a pulse radiolysis of the respective potassium salts have been used to study the tryptophan residues of the glucoenzyme, glucoamylase I (EC 3.2.1.3.). At neutral pH, Br2.- reacted with the tryptophan residues of glucoamylase I as expected from previous studies of proteins and free amino acids. However, (SCN)2.- at neutral and high pH was surprisingly unreactive towards the native enzyme. Reaction did occur, however, between (SCN)2.- and glucoamylase from which one-third of the covalently bound carbohydrate had been removed, producing a tryptophyl radical. Reaction also occured between (SCN)2.- and glucoamylase I inactivated by treatment with sodium dodecyl sulphate, but the tryptophan residues were not involved. It is concluded from the results that two 'types' of tryptophan residues are found in glucoamylase I; both are attacked by Br2.- but only one type is attacked by (SCN)2.-.
mesh_terms: D000838:Anions; D001234:Aspergillus niger / Q000201:enzymology*; D001965:Bromides; D004789:Enzyme Activation; D005609:Free Radicals; D005087:Glucan 1,4-alpha-Glucosidase; D005959:Glucosidases; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D013861:Thiocyanates; D014364:Tryptophan
chemical_list: D000838:Anions; D001965:Bromides; D005609:Free Radicals; D013861:Thiocyanates; D014364:Tryptophan; D005959:Glucosidases; D005087:Glucan 1,4-alpha-Glucosidase