Specific and selective degradation of protein by illumiation

光系统II反应中心D1蛋白在强光照射、光抑制过程中被选择性和特异性降解。Q_A功能的丧失是光抑制导致光系统II功能丧失的主要原因。各种类型的光系统II抑制剂的存在可抑制或刺激光抑制，这表明抑制剂结合q_b结合位点的变化调节了D1蛋白的降解。事实上，D1蛋白的裂解是在光系统II抑制剂PNO8 （n -辛基-3-硝基-2,4,6-三羟基苯甲酰胺）存在的完全黑暗下进行的。在另一种PS II抑制剂DCMU的存在下，裂解被抑制，表明PNO8在q_b位点的结合参与了裂解反应。在D1蛋白去环区Lue 258附近的一个位点进行切割，得到23和9 kDa片段，这些片段也在强光照射下的光抑制过程中发现。在低温和丝氨酸型蛋白酶抑制剂的作用下，卵裂被抑制，但不受氧气存在的影响。解理不需要光，但由短时间的预照明触发。结果表明，光照下q_b结合位点的改变和PNO8的结合诱导了D1蛋白的裂解反应。

A photosystem II reaction center D1 protein was slelctively and specifically degraded during the course of strong light illuminaition, photoimhibition. The loss of the function of Q_A was primarily responsible for the loss of the photosystem II function by photoinhibition. The photoinhibition was sppressed or stimulated by the presence of varios type photosytem II inhibitors, suggesting that the changes in the Q_B-binding site by the binding of the inhibitors modulates the degradation of the D1 protein. In fact, the cleavage of the D1 protein was prrformed under complete darkness in the presence of photosystem II inhibitor, PNO8 (N-octyl-3-nitro-2,4,6-trihydroxy benzamide). The cleavage was inhibited in the presence of other PS II inhibitor, DCMU,indicating that the binding of PNO8 in the Q_B-site is responsible for the cleavage reaction. The cleavage was performed at one site in the vicinity of Lue 258 in the de-loop region of the D1 protein to give 23 and 9 kDa fragments that are also found during photoinhibition by illuminating strong light. The cleavege was inhibiet under low temperature and inhibitors of serine type protease but was not affected by the presence of oxygen. The cleavage did not require light but was triggered by short time pre-illumination. The results suggest that some changes in the Q_B-binding site by illumination and the binding of PNO8 induce the state which allows the cleavage reaction of the D1 protein.