Selective free radical reactions with proteins and enzymes: a reversible equilibrium in the reaction of (SCN)2-

Reaction of (SCN)2- with lysozyme has been studied by pulse radiolysis and in inactivation measurements. The principal reactive sites towards (SCN)2- in lysozyme are tryptophan residues. In both series of experiments, the reaction has been observed to be suppressed by low pH values and high thiocyanate concentrations. The results obtained are consistent with a reversible free-radical equilibrium between thiocyanate and tryptophan radicals in lysozyme, as reported previously with free tryptophan by Posener et al. (1976). (author)