2,3-Butanedione as a photosensitizing agents: application to α-amino acids and α-chymotrypsin

Abstract

2,3-Butanedione sensitized the rapid photodestruction of free α-amino acids, and the photoinactivation of α-chymotrypsin, in the presence of ultraviolet light and oxygen. These reactions showed "pseudo-first-order" kinetics at 2,3-butanedione concentrations approximating those employed for the chemical modification of arginine residues in proteins. The photoreactions were inhibited in anoxic media or in the presence of azide; findings were consistent with a singlet oxygen mechanism for these reactions. No enhancement in the rate of reaction was observed in D2O. The rate of 2,3-butanedione-sensitized photodestruction of free amino acids increased with increasing pH. However, the rate constants for the photosensitized inactivation of α-chymotrypsin, as well as those for the photodestruction of the tryptophan residues of this enzyme, decreased linearly with increasing pH.