Assignment of the spectra of protein radicals in cytochrome c peroxidase

In oxidized cytochrome c peroxidase a peak at 570 nm has been attributed to an intermediate tryptophan free radical of indeterminate protonation state. Ab initio calculations of the spectra of the neutral and cationic free radicals of the indole side chain of tryptophan are used to assign the absorption spectra to the neutral radical. Earlier assignment attempts were confused by the large blue shift in water of the in vacuo transition. The relevant calculated transitions of both the neutral and cationic indole radicals, in fact, shift substantially to the blue in aqueous solution