Utsumi S, Okada M, Udaka K, Amano T
Mol Immunol. 1985 Jul;22(7):811-9. doi: 10.1016/0161-5890(85)90147-6.
A number of fragments derived from acid-treated rabbit IgG by digestion with plasmin have been separated by high-resolution gel filtration. Fragments isolated included a dimer and monomer Facb, named F(acb)2 and Facb, respectively and a heterodimer composed of Facb and Fab subunits, named F(acb)(ab). A C gamma 2 fragment was obtained by papain digestion of Facb. A heterodimer composed of Facb and Fab', named F(acb)(ab'), was also prepared by oxidizing a reduced mixture of these fragments. Fragments thus obtained are classified into two groups--those carrying paired C gamma 2 domains, i.e. F(acb)2, and the disulfide-linked dimeric C gamma 2 fragment; and those having a single C gamma 2 domain, i.e. reduced, alkylated Facb and C gamma 2 fragment, F(acb)(ab) and F(acb)(ab'). These fragments exhibited marked differences in their capacity to activate complement in assay systems of hemolysis and complement consumption by immune complexes or aggregates on polystyrene latex. Fragments of the former group could activate complement but with a definitely reduced efficiency (50%) compared to intact IgG, whereas fragments of the latter group were practically inactive. Although it was not determined whether the C1-binding capacity itself is changed by monomerization of the C gamma 2 domain, the results suggested that the intact paired C gamma 2 module is required at least for the activation process of complement.
通过纤溶酶消化酸处理的兔IgG得到的一些片段已通过高分辨率凝胶过滤分离。分离出的片段包括一个二聚体和单体Facb，分别命名为F(acb)2和Facb，以及一个由Facb和Fab亚基组成的异二聚体，命名为F(acb)(ab)。通过木瓜蛋白酶消化Facb获得了一个Cγ2片段。还通过氧化这些片段的还原混合物制备了一个由Facb和Fab'组成的异二聚体，命名为F(acb)(ab')。由此获得的片段分为两组——那些携带配对Cγ2结构域的片段，即F(acb)2和二硫键连接的二聚体Cγ2片段；以及那些具有单个Cγ2结构域的片段，即还原的、烷基化的Facb和Cγ2片段、F(acb)(ab)和F(acb)(ab')。在溶血和免疫复合物或聚苯乙烯乳胶上的聚集体消耗补体的检测系统中，这些片段在激活补体的能力上表现出明显差异。前一组片段可以激活补体，但与完整IgG相比效率明显降低(50%)，而后一组片段实际上没有活性。虽然没有确定C1结合能力本身是否因Cγ2结构域的单体化而改变，但结果表明完整的配对Cγ2模块至少是补体激活过程所必需的。
