Tyrosine YZ and YD of photosystem II -: Comparison of optical spectra to those of tyrosine oxidised by pulsed radiolysis

We have compared the optical spectrum of tyrosine oxidised in aqueous solution by pulsed radiolysis with spectra of redox active tyrosines Y-Z and Y-D of photosystem II. This indicates a "tyrosinate" state for these tyrosines and also casts doubt on the assumption that Y-Z and Y-D optical spectra are very similar in different photosystem II preparations. It suggests that further optical spectra of Y-Z in more intact oxygen-evolving preparations are needed before the role of Y-z in water oxidation can be clarified. (C) 1998 Elsevier Science B.V.