A steady‐state reversible signal peaking at 680 nm in the red region of the light‐dark difference spectrum has been generated in the isolated D1/D2 photosystem II reaction centre using silicomolybdate as an electron acceptor. The signal is dependent on the structural integrity of the reaction centre and is probably due to the formation of P680+resulting from oxidation of the primary donor, thought to be a chlorophylladimer. The spectral shape of the red band of the difference spectra, however, contains a shoulder at 672 nm which suggests that monomeric chlorophyll within the reaction centre may also be photooxidised. Prolonged illumination of the sample with bright white light causes a selective bleaching of the long‐wavelength absorbing form of chlorophyll within the reaction centre. Protection against this photodestruction of P680 occurs when silicomolybdate is present during the preillumination.
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Telfer et al. (1989) studied this question.