Free radical inactivation of trypsin

Abstract

Reactivities of free radical oxidants, .OH, Br -· 2 and Cl 3COO . and a reductant, CO -· 2, with trypsin and reactive protein components were determined by pulse radiolysis of aqueous solutions at pH 7, 20°C. Highly reactive free radicals, .OH, Br -· 2 and CO -· 2, react with trypsin at diffusion controlled rates, k( .OH + trypsin) = 8.2 × 10 10 M -1 s -1, k(Br -· 2 + trypsin) = 2.55 × 10 9 M -1 s -1 and k(CO -· 2 + trypsin) = 2.6 × 10 9 M -1 s -1. Moderately reactive trichloroperoxy radical, k(Cl 3COO . + trypsin) = 3 × 10 8 M -1 s -1, preferentially oxidizes histidine residues. The efficiency of inactivation of trypsin by free radicals is inversely proportional to their reactivity. The yields of inactivation of trypsin by .OH, Br -· 2 and CO -· 2 are low, G(inactivation) = 0.6-0.8, which corresponds to ∾ 10% of the initially produced radicals. In contrast, Cl 3COO . inactivates trypsin with ∾ 50% efficiency, i.e. G(inactivation) = 3.2.