Radiation induced modification of tryptophan and tyrosine residues in flavocytochrome b(2) in dilute aqueous solution

Steady state gamma irradiation of an aqueous solution of flavocytochrome b( 2) under different conditions led to modification of tryptophan and tyrosin e residues. These aromatic amino acid residues were more susceptible to the attack by OH radicals than H atoms. Unchanged quantum yield values for try ptophan and tyrosine residues and unchanged tryptophan excited state lifeti me in the irradiated enzyme suggests that irradiation results in breakage o f some non-covalent bonds disrupting the peptide framework partially. It is justified by the circular dichroic studies for the irradiated enzyme which shows a reduced helicity but no evolution towards any other structures. (C ) 2000 Elsevier Science Ltd. All rights reserved.