FREE-RADICAL INACTIVATION OF PEPSIN

Alkylperoxy radicals containing one, two or three chlorine atoms, .CO2 -, O2.- and HO2. were reacted with pepsin in aqueous solutions. It was found that only Cl3COO. and .CO2- inactivate pepsin, attacking prefer entially the disulfide bridge. Transient spectra obtained upon complet ion of the Cl3COO. + pepsin reaction at pH 5 indicate that 20% of init ially produced Cl3COO. radicals oxidizes tryptophan residues, and 40% disulfide bridges. The inactivation induced by the Cl3COO. radical inc reases at lower pH, and the maximal inactivation, G(in) = 5.8, was obs erved at pH 1.5. The inactivation of pepsin by .CO2- radicals depends on the absorbed dose. The maximal inactivation, G(in) = 4.5, was deter mined in the dose range from 38 to 53 Gy.