UV radiation effects on flavocytochrome b(2) in dilute aqueous solution

A dilute aqueous solution of flavocytochrome b(2) when exposed to inactivat ing doses of UV radiation at 280 nm underwent reversible loss in activity b oth under aerated and deaerated conditions. The active site as well as the substrate binding sites were found to be modified in the irradiated enzyme. Irradiation of the enzyme in the UV-C range resulted in partial unfolding of the polypeptide framework. Destruction and/or modification of both trypt ophan and tyrosine residues as well as heme moieties took place. Preliminar y laser flash photolysis studies suggest that the initial photo-ionization takes place with tryptophan and tyrosine residues with the formation of exc ited states and radicals, and then rapid transfer of electrons takes place to histidyl and cystinyl sites which might have eventually been altered in the process. (C) 2000 Elsevier Science B.V. All rights reserved.