Dye-sensitized photo-oxidation of pig kidney Dopa decarboxylase

The effects of irradiation of pig kidney Dopa decarboxylase by visible light absorbed by the intrinsic chromophore, pyridoxal-P, and by the externally added dyes, pyridoxal-P or proflavin, have been studied. In all cases inactivation was observed, even though to different extens, which seemed to be essentially correlated to tryptophanyl residues photodestruction. Kinetics of inactivation and oxidation of these amino acid residues revealed the presence of two distinct groups of tryptophan residues with different photooxidation rate constants. A different role for these classes of residues in the structure and function of Dopa decarboxylase has been suggested.