THE DESTRUCTION OF TRYPTOPHANYL RESIDUES IN TRYPSIN BY 280-nm RADIATION

Abstract— The destruction of tryptophanyl residues in trypsin by 280-nm radiation was studied in relation to enzyme inactivation. Quantum yields for destruction of this residue (determined using the pDAB reagent) and for the inactivation of trypsin were measured when the enzyme was exposed to different environmental perturbations. The conformational modifications of trypsin induced in 6 M guanidine-HCl did not alter the rates of tryptophan destruction and enzyme inactivation. However, an enhanced destruction of the tryptophanyl residues was observed when trypsin solutions were irradiated at 60°C in the presence of air. The increased rate of tryptophan destruction at this temperature was not accompanied by a corresponding increase in the inactivation quantum yield. It was concluded that any photochemically induced reactions of this chromophore that are sensitive to conformational modifications or that result in the destruction of the indole ring are not important in the inactivation mechanism of trypsin.