Science. 1989 May 12;244(4905):702-5. doi: 10.1126/science.244.4905.702.
The structure of L(8)S(8) RuBisCo (where L is the large subunit and S is the small subunit) from spinach has been determined to a resolution of 2.8 ångstrom by using fourfold averaging of an isomorphous electron density map based on three heavy-atom derivatives. The structure of the S subunit is different from that previously reported for the tobacco S subunit in spite of 75 percent sequence identity. The elements of secondary structure, four antiparallel beta strands and two alpha helices, are the same, but the topology and direction of the polypeptide chain through these elements differ completely. One of these models is clearly wrong. The spinach model has hydrophobic residues in the core between the alpha helices and beta sheet as well as conserved residues in the subunit interactions. The deletion of residues 49 to 62 that is present in the Anabaena sequence removes a loop region in the spinach model. The positions of three mercury atoms in the heavy-atom derivatives agree with the assignment of side chains in the spinach structure.
菠菜 L(8)S(8)RuBisCo（其中 L 是大亚基，S 是小亚基）的结构已通过基于三个重原子衍生物的四分之一同晶电子密度图的平均化，以 2.8 ångstrom 的分辨率确定。尽管序列同一性为 75％，但 S 亚基的结构与先前报道的烟草 S 亚基不同。二级结构元件，即四个反平行的β链和两个α螺旋，相同，但多肽链通过这些元件的拓扑结构和方向完全不同。其中一个模型显然是错误的。菠菜模型在α螺旋和β片之间的核心区域具有疏水性残基以及亚基相互作用中的保守残基。在 Anabaena 序列中存在的 49 到 62 个残基的缺失除去了菠菜模型中的一个环区。重原子衍生物中的三个汞原子的位置与菠菜结构中侧链的分配一致。
