DONOR-SIDE PHOTOINHIBITION IN PHOTOSYSTEM-II FROM CHLAMYDOMONAS-REINHARDTII UPON MUTATION OF TYROSINE-Z IN THE D1 POLYPEPTIDE TO PHENYLALANINE

When tyrosine-Z of the D1-polypeptide of the photosystem II from Chlam ydomonas reinhardtii was changed to phenylalanine, the rapid donor to P-680(+) was lost, and P-680(+) accumulated on illumination, The rapid donation from tyrosine-Z was replaced by a slow electron transfer fro m an endogenous donor, Spectrophotometric measurements showed that car otenoids and chlorophylls were bleached by the P-680(+) either directl y or indirectly upon illumination, The carotenoid bleaching was inhibi ted in the presence of SOD or catalase, but the reaction did not requi re molecular oxygen as an electron acceptor, These observations led us to conclude that active oxygen radicals, possibly hydroxyl radicals, take part in the destruction of carotenoids in the Y161F mutant, Possi ble mechanisms for the destruction are discussed.