Role of arginine in substrate binding and tryptophan microenvironment 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 and the kinetics of modification revealed the involvement of a guanidinium group in the catalytic function of the enzyme. The failure of the substrate to quench the fluorescence of the Arg modified enzyme indicates the involvement of Arg in substrate binding. Modification of Trp by N-bromosuccinimide leads to inactivation of the enzyme through peptide cleavage although substrate binding quenches the enzyme fluorescence. Analysis of quenching of enzyme fluorescence by collisional quenchers viz. acrylamide, potassium iodide and cesium chloride suggests that all the Trp residues are located in a similar moderately hydrophobic environment.