光系统Ⅱ反应中心D_1/D_2/cyt b_(559)复合物光破坏的多步反应

MULTI-STEP REACTION OF PHOTOSYSTEM Ⅱ REACTION CENTER D_1/D_2/CYT OCHROME B_(559) COMPLEX DURING PHOTODAMAGE

光系统Ⅱ(PSⅡ)反应中心D_1D_2’cyt b_(559)复合物在强光照射下色素分子受到破坏,导致在红区(Q_y带)的吸光度值及CD信号的下降,而且在光照后的暗放置过程中这种变化继续进行,吸收差光谱的峰位在680nm处,说明受破坏的很可能是原初电子供体P680.在光照后的暗放置过程中,该反应中心复合物的荧先强度继续升高,而且峰位蓝移.所有这些结果表明,在光照的过程中,PSⅡ反应中心D_1/D_2/cytb_(559)复合物很可能有一个相对稳定的反应中间体形成,从而造成在暗放置过程中该反应中心继续受到破坏,也就是说,PSⅡ反应中心D_1/D_2/cytb_(559)复合物的光破坏不是一步反应,而是一个多步反应.

Photosystem II reaction center D1/D2/cyt b559 complex is easily damaged by strong illumination, which results in the decrease of absorbance and CD signal in the red region (Qy band). During the incubation in the dark following illumination, the decrease continually proceeds. The absorption difference spectra peak at 680nm indicates that it is probably the primary electron donor P680 which is damaged. Fluorescence emission intensity increases and maximum emission wavelength blue-shifts in the dark incubation after proillumination. All these results suggest that a relative stable intermediate is likely generated by illumination, resulting in the further damage of the reaction center in the dark incubation. That is, the photodamage of the isolated photosystem II reaction center D1/D2/cyt b559 complex is not just a one-step reaction, but a multi-step reaction.