Mayer F, Wallace J C, Keech D B
Eur J Biochem. 1980 Nov;112(2):265-72. doi: 10.1111/j.1432-1033.1980.tb07202.x.
Using negative staining and electron microscopic tilting techniques in conjunction with modelling experiments, the fine structure of chicken, sheep and rat pyruvate carboxylases has been studied. The overall configuration appears to be a tetrahedron-like structure consisting of two pairs of subunits in two different planes orthogonal to each other with the opposing pairs of subunits interacting with each other on their convex surfaces. The predominant form of the enzyme particles mounted and stained in the presence of acetyl-coenzyme A consisted of a compact, triangular outline enclosing three readily visible intensity maxima. When samples were mounted in the absence of acetyl-coenzyme A the molecules were more 'open' predominantly rhomboid structures. From tilting experiments it is concluded that the rhomboid images found in the absence of acetyl-coenzyme A represent partly or wholly flattened forms of the tetrahedron-like molecule. A feature of the enzyme when mounted in the absence of acetyl-coenzyme A was the existence of a 'cleft' along the longitudinal midline of each subunit, suggesting that the subunits may consist of two distinct domains.
结合建模实验，使用负染色和电子显微镜倾斜技术，对鸡、绵羊和大鼠丙酮酸羧化酶的精细结构进行了研究。整体构型似乎是一种四面体样结构，由两对亚基组成，这两对亚基位于两个相互正交的不同平面中，相对的亚基对在其凸面上相互作用。在乙酰辅酶A存在的情况下进行固定和染色的酶颗粒的主要形式是紧凑的三角形轮廓，包围着三个易于观察到的强度最大值。当样品在没有乙酰辅酶A的情况下进行固定时，分子更“开放”，主要呈菱形结构。从倾斜实验得出的结论是，在没有乙酰辅酶A的情况下发现的菱形图像代表四面体样分子的部分或完全扁平形式。当在没有乙酰辅酶A的情况下进行固定时，该酶的一个特征是沿着每个亚基的纵向中线存在一个“裂缝”，这表明亚基可能由两个不同的结构域组成。
