Greenberg B M, Gaba V, Mattoo A K, Edelman M
Department of Plant Genetics, Weizmann Institute of Science, Rehovot, Israel.
EMBO J. 1987 Oct;6(10):2865-9. doi: 10.1002/j.1460-2075.1987.tb02588.x.
The 32 kd photosystem II protein of plant chloroplasts is rapidly turned over in the light. The initial events in the degradation of the 32 kd protein were studied. A 23.5 kd breakdown product was identified in Spirodela oligorrhiza membranes using immunological analysis. The 23.5 kd polypeptide was shown to be derived from the amino-terminal portion of the 32 kd protein using partial proteolytic fingerprinting. An in vivo precursor--product relationship between the 32 kd protein and the 23.5 kd polypeptide was kinetically demonstrated by radiolabeling and pulse-chase experiments. The cleavage site yielding the 23.5 kd polypeptide was localized to a functionally active region (between helices IV and V) of the 32 kd protein. We propose that an alpha-helix-destabilizing 'degradation' sequence, bordered by arginine residues 225 and 238, is involved in the formation of the 23.5 kd polypeptide.
植物叶绿体中32kd的光系统II蛋白在光照下迅速周转。对32kd蛋白降解的初始事件进行了研究。利用免疫分析在少根紫萍膜中鉴定出一种23.5kd的降解产物。使用部分蛋白水解指纹图谱显示，23.5kd的多肽源自32kd蛋白的氨基末端部分。通过放射性标记和脉冲追踪实验从动力学上证明了32kd蛋白与23.5kd多肽之间的体内前体-产物关系。产生23.5kd多肽的切割位点定位于32kd蛋白的功能活性区域（螺旋IV和V之间）。我们提出，由精氨酸残基225和238界定的α-螺旋不稳定“降解”序列参与了23.5kd多肽的形成。
