The photodamage and protective role of pheophytin a in the photosystem II reaction center against light-induced damage

摘要

Light is the only energy source for photosynthesis, but excess light energy is harmful to plants. During the recent years, especially since the preparation of PS II (PS II) reaction center Dl/D2/Cyt b-559 complex in 1987 by Nanba and Satoh, the molecular processes of photoinhibition have been intensively studied and great development has been made. The detailed mechanism of photoinhibition has been an important topic. The photobleaching at 680 nm in visible absorption and circular dichroism spectra are usually attributed to the photodamage of P680 in the PS II reaction center. Beacuse of the overlapping of absorption of P680 and pheophytin (Pheo) in the PS II reaction center, the photodamage of Pheo is probably involved. Our recent papers have reported that the content of Pheo a decreased about 47% by strong illumination using high performance liquid chromatography, which suggests only one of the two Pheo a molecules in the PS II reaction center complex was damaged. The damaged pheophytin, which is not associated with the photochemical activity, is probably bound to D2 polypeptide based on the homology between the reaction center of PS II and that of purple bacteria. However, the detailed molecular mechanism of Pheo damage is not clear.