Beitel G J, Luft A J, Panrucker D E, Lorscheider F L
Biochem J. 1986 Sep 1;238(2):359-64. doi: 10.1042/bj2380359.
High resolution images of rat acute-phase alpha 2-macroglobulin (AP alpha 2M) have been obtained by using dark-field electron microscopy. No staining or artifact-inducing procedures were used. Analysis of unfiltered electron microscope plates, exposed to minimal electron beam radiation, revealed highly contrasted particles of variable morphology with dimensions of approx. 19 nm X 14 nm. An electron-dense core with four to six projections could be seen. Two-fold symmetry was evident in selected images, supporting the four-subunit composition of the protein. Image processing and filtering confirmed the presence and configuration of the projections by demonstrating exact molecular dimensions of 16 nm X 9.5 nm and a shape with six projections like that of the Russian letter zh. SDS/polyacrylamide-gel electrophoresis revealed that this molecule was in the proteinase-bound form. C.d. data revealed a surprisingly low content of alpha-helical secondary structure (12%) and an atypically large content of beta-form structure (33%). Comparison of the amino acid compositions of AP alpha 2M and human alpha 2-macroglobulin indicated a high degree of homology between the two molecules. It is concluded that the conformation of rat AP alpha 2M, both at the molecular and secondary structural levels, is strikingly similar to that of human alpha 2-macroglobulin.
通过暗场电子显微镜获得了大鼠急性期α2-巨球蛋白（APα2M）的高分辨率图像。未使用染色或诱导假象的程序。对暴露于最小电子束辐射的未过滤电子显微镜底片进行分析，发现了形态各异、对比度高的颗粒，尺寸约为19纳米×14纳米。可以看到一个有四到六个突起的电子致密核心。在选定的图像中明显存在二重对称性，这支持了该蛋白质的四亚基组成。图像处理和滤波通过显示精确的分子尺寸16纳米×9.5纳米以及具有六个类似俄语字母ж形状的突起，证实了突起的存在和构型。SDS/聚丙烯酰胺凝胶电泳显示该分子处于蛋白酶结合形式。圆二色性数据显示α-螺旋二级结构的含量出奇地低（12%），β-形式结构的含量异常高（33%）。APα2M和人α2-巨球蛋白的氨基酸组成比较表明这两种分子之间具有高度同源性。得出的结论是，大鼠APα2M在分子和二级结构水平上的构象与人类α2-巨球蛋白的构象惊人地相似。
