Mihaesco C, Seligmann M
J Exp Med. 1968 Mar 1;127(3):431-53. doi: 10.1084/jem.127.3.431.
Papain digestion of two Waldenström IgM globulins produced a high amount of small peptides and resulted in the formation of two end products, the Fabmicro and Fcmicro fragments. The Fcmicro fragment is characterized by a fast electrophoretic mobility, a high content in carbohydrate, and a high molecular weight. It was demonstrated that this fragment is made of heavy chain pieces belonging to several disulfide-linked monomeric subunits, presumably representing the carboxy-terminal end of the micro-chains. Fc fragments from the two macroglobulins could not be distinguished immunologically. An appreciable proportion of IgM molecules apparently underwent degradation without the formation of a stable Fc fragment. An Fc-like fragment, analogous to the reduced Fc fragment, was obtained at early stages of papain digestion of the IgM subunits. The Fabmicro fragment, with slow and individually distinct electrophoretic mobility, bears many physicochemical and immunological similarities to the Fabgamma fragment. It consists of one light chain and one Fd piece, both of which were isolated. The interaction of these two constituents was demonstrated by gel diffusion studies. Fab fragments of both IgM globulins were resolved into two subpopulations with different electric charges. In addition to these fragments, intermediary split products were observed at early stages of the degradation process, together with a high yield of small peptides mainly derived from the papain-sensitive region of the heavy chains. Immunologic data strongly suggested that this segment of micro-chains is situated between the Fd piece and the portion included in the Fc fragment. Several experiments indicated the importance of conformational antigenic specificity in both Fab and Fc regions of the IgM globulins.
木瓜蛋白酶对两种瓦尔登斯特伦 IgM 球蛋白的消化产生了大量小肽，并导致形成了两种终产物，即 Fabmicro 和 Fcmicro 片段。Fcmicro 片段的特征在于电泳迁移速度快、碳水化合物含量高以及分子量高。已证明该片段由属于几个二硫键连接的单体亚基的重链片段组成，推测代表微链的羧基末端。来自两种巨球蛋白的 Fc 片段在免疫学上无法区分。相当一部分 IgM 分子显然经历了降解，没有形成稳定的 Fc 片段。在 IgM 亚基的木瓜蛋白酶消化早期获得了一种类似于还原 Fc 片段的 Fc 样片段。Fabmicro 片段具有缓慢且各自不同的电泳迁移率，在物理化学和免疫学方面与 Fabgamma 片段有许多相似之处。它由一条轻链和一个 Fd 片段组成，两者均已分离。通过凝胶扩散研究证明了这两种成分之间的相互作用。两种 IgM 球蛋白的 Fab 片段都被分解为两个具有不同电荷的亚群。除了这些片段外，在降解过程的早期还观察到中间裂解产物，以及主要来自重链木瓜蛋白酶敏感区域的大量小肽。免疫学数据强烈表明，微链的这一部分位于 Fd 片段和 Fc 片段所含部分之间。多项实验表明构象抗原特异性在 IgM 球蛋白的 Fab 和 Fc 区域都很重要。
