The radiolysis of protein A

Abstract The effects of ionising radiations on the activity of protein A from Staphylococcus aureus has been investigated. Reaction with H , OH and e − aq results in loss of protein A activity, the values of the inactivating efficiencies being 0.016, 0.003 and 0.0014 respectively. Reaction with (SCN) − 2 increases the rate of the inactivation process (inactivating efficiency=0.007), compared to that of OH radical. This latter species, as well as OH, destroy tyrosine residues (as is evidenced by a progressive loss of tyrosine fluorescence) and is accompanied by formation of a tyrosine-linked protein A dimer. The dimer has been isolated using FPLC and shows no activity towards IgG.