Department of Biological Chemistry, Hebrew University, Jerusalem, Israel.
EMBO J. 1985 Jul;4(7):1655-9. doi: 10.1002/j.1460-2075.1985.tb03833.x.
The 32 000-dalton Q(B)-protein of photosystem II (PS II) is rapidly damaged and removed from isolated pea thylakoids during incubation in the light resulting in a loss of photosynthetic electron flow through PS II. This in vitro photoinhibition is similar to that previously reported with intact Chlamydomonas cells. The damage occurs at a faster rate in vitro, however, due to the inability of isolated thylakoids to synthesize replacement Q(B)-protein. The removal of the damaged Q(B)-protein does not require any soluble components of the chloroplast stroma and is unaffected by the protease inhibitors phenyl-methylsulfonylfluoride or antipain. Unlike the effect of trypsin, no low mol. wt. membrane-bound or soluble fragments of the labelled Q(B)-protein could be identified either by autoradiography or immunologically using polyclonal antibodies specific for the Q(B)-protein. The lightinduced damage to the Q(B)-protein (indicated by a loss of Q(B) functional activity), preceded the removal of the protein from the membrane. We conclude that photodamage of the Q(B)-protein generates a conformational change which renders the protein susceptible to attack by a highly efficient, intrinsic membrane protease.
类囊体蛋白复合体 II(PS II)的 32000 道尔顿 Q(B)-蛋白,在光照下于分离的豌豆类囊体中孵育时会迅速受损并从膜上脱落,导致 PS II 中的光合电子流丧失。这种体外光抑制与先前用完整衣藻细胞报告的情况相似。然而,由于分离的类囊体无法合成替代的 Q(B)-蛋白,体外的损伤速度更快。受损的 Q(B)-蛋白的去除不需要叶绿体基质中的任何可溶性成分,并且蛋白酶抑制剂苯甲基磺酰氟或抑蛋白酶肽对其没有影响。与胰蛋白酶的作用不同,用针对 Q(B)-蛋白的多克隆抗体进行放射自显影或免疫检测,均未发现标记的 Q(B)-蛋白的任何低分子量膜结合或可溶性片段。光诱导的 Q(B)-蛋白损伤(表现为 Q(B)功能活性丧失)先于蛋白从膜上脱落。我们的结论是,Q(B)-蛋白的光损伤会产生构象变化,使蛋白容易受到高效的内在膜蛋白酶的攻击。