Degradation of RuBisCO in the Leaves of Crop Plants During Senescence

Rubisco(核酮糖-1，5-二磷酸羧基酶/加氧酶)是光合作用固定CO_2的重要酶，其在绿叶中的含量占可溶性蛋白质的50%。已有研究表明Rubisco可以在叶绿体中被降解。在这项国际科学研究中，我们研究了从小麦(US)、大麦(Huffaker‘s group)和黑麦草(Thomas’s group)叶片中机械分离和纯化的叶绿体中Rubisco的降解情况。(1989年)。这种活性是由十二烷基硫酸钠刺激的(Yokota et al.1990年)。然而，这些降解产物与Rubisco与从相似叶片中纯化的液泡孵育时得到的产物非常相似。经热裂解素预处理的叶绿体对Rubisco没有蛋白分解活性。这些结果表明，对Rubisco的前溶活性为I…。更多的叶绿体主要是由于分离过程中附着在叶绿体外膜上的液泡蛋白水解酶的污染(Miyadai等人。然而，通过增加应用于蛋白质印迹的叶绿体蛋白的数量，可以检测到新的多肽。这些多肽与V-8酶孵育后的许多斑点与Rubisco中的相同，表明这些新的多肽是Rubisco的部分降解产物。此外，这些多肽的存在与热裂解处理无关。因此，这些结果有力地表明在叶绿体(铃木，正在准备)中存在蛋白酶(S)。光胁迫下的叶片衰老具有与遮荫植物类似的类囊体蛋白的一些调节变化(Hidema等人)。提交，Mae等人。正在准备中)。然而，无论光胁迫如何，衰老过程中基质酶的下降总是表现出很强的相关性。这些结果可能表明，叶绿体基质中包括Rubisco在内的每种酶都不存在选择性降解机制(Hidema等人。因此，我们认为Rubisco可能被叶绿体中的非选择性蛋白水解酶(S)降解。较少

Rubisco (ribulose-1, 5-bisphosphate carboxylase/oxygenase) is an important enzyme for photosynthetic CO_2 fixation, and its amount in green leaves accounted for 50% of the soluble protein. It has been suggested that Rubisco can be degraded within chloroplasts. In this International ScientificResearch, we examined on the degradation of Rubisco in the chloroplasts isolated mechanically and purified from wheat (us), barley (Huffaker's group) and Lorium (Thomas' group) leaves.Rubisco-degradation activity in the chloroplasts was very weak and its degradation could be detected only by applying Western blotting (Mae et al. 1989). This activity was stimulated by SDS (Yokota et al. 1990). However, the degradation products were very similar to those obtained when Rubisco was incubated with the vacuoles purified from like leaves. Chloroplasts, which had pretreated with thermolysin, had no proteolytic activity against Rubisco. These results show that the prteolytic activity against Rubisco found i … More n the chloroplasts was mostly due to the contamination of vacuole proteases adhering to the outer envelope of chloroplasts during isolation (Miyadai et al. 1990).By increasing the amount of chloroplast proteins applied for Western blotting, however, new polypeptides could be detected. Many spots of these polypeptides after incubation with V-8 protease corresponded to those from Rubisco, indicating that the new polypeptides are some of the degradation products of Rubisco. In addition, the existence of these peptides was independent of thermolysin treatment. Thus, these results strongly suggested the existence of protease (s) in the chloroplasts (Suzuki, in preparation).Leaf senescence under light stress had some of the regulatory changes in the thylakoid proteins similar to those of shade plants (Hidema et al. submitted, Mae et al. in preparation). However, declines in stromal enzymes during senescence always show a strong correlation one another irrespective of lght stress. These results may suggest that there is no selective degradation mechanism for each enzyme including Rubisco in chloroplast stroma (Hidema et al. submitted).Thus, we consider that Rubisco may be degraded by non-selective proteolytic enzyme (s) in the chloroplasts. Less