CATALYTIC THIOL AND CARBOXYLATE - ROLE OF CYSTEINE AND GLUTAMIC-ACID IN THE XYLOSIDIC ACTIVITY OF ENDOXYLANASE FROM CHAINIA SP. (NCL 82-5-1)

Chemical modification of the endoxylanase from Chainia sp. with group- specific chemical modifiers in the absence and presence of substrate a nd kinetics of modification revealed the involvement of a thiol and a carboxylate in the catalytic function of the enzyme. The active-site p eptides were chemically labeled and sequenced. The sequence alignment of the chemically labeled peptide with other family G/11 xylanases sho wed that the catalytic glutamate of Chainia xylanase is located in a h ighly homologous region and may function as an acid/base catalyst whil e thiol of the Cys may function as a nucleophile. (C) 1998 Academic Pr ess.