Seya T, Okada M, Hazeki K, Nagasawa S
Department of Immunology, Center for Adult Diseases, Osaka, Japan.
Mol Immunol. 1991 Apr-May;28(4-5):375-82. doi: 10.1016/0161-5890(91)90150-i.
Two proteins that are involved in cleavage of methylamine-treated C3 of guinea-pig origin (C3(MA)gp) have been isolated from guinea-pig serum. One of them functioned as a cofactor of human factor I (Ihu) for cleavage of C3(MA)gp and its molecular size was 150 kDa. The other was functionally pure and able to cleave C3(MA)gp together with human factor H (Hhu). They appear to be analogous to human factors H and I in the guinea-pig and will be referred to as Hgp and Igp. Methylamine-treated human C3 [C3(MA)hu] was not a compatible substrate for Hgp or Igp: little cleavage of C3(MA)hu was observed if human factor H (Hhu) or I was substituted with the guinea-pig counterpart. C3(MA)gp, on the other hand, served as a substrate, though less efficiently, for Hhu and Ihu. Human C4b-binding protein (C4bp) and membrane cofactor protein (MCP) as well as Hhu could participate in cleavage of C3(MA)gp by Igp or Ihu. In these assays, C3(MA)gp was degraded again less efficiently than C3(MA)hu. Interestingly, human C3b/C4b receptor (CR1) mediated factor I-dependent cleavage of C3(MA)hu and C3(MA)gp to a similar extent regardless the sources of factor I. These results suggest that factor I-dependent C3b regulatory system is species-specific except in the case of CR1, which may function as a cofactor irrespective of species.
从豚鼠血清中分离出了两种参与裂解豚鼠来源的经甲胺处理的C3（C3(MA)gp）的蛋白质。其中一种作为人I因子（Ihu）裂解C3(MA)gp的辅助因子，其分子大小为150 kDa。另一种在功能上是纯的，能够与人H因子（Hhu）一起裂解C3(MA)gp。它们似乎类似于豚鼠体内的人H因子和I因子，将被称为Hgp和Igp。经甲胺处理的人C3 [C3(MA)hu] 不是Hgp或Igp的合适底物：如果用人H因子（Hhu）或I因子替换为豚鼠对应的因子，则观察到C3(MA)hu的裂解很少。另一方面，C3(MA)gp虽然效率较低，但可作为Hhu和Ihu的底物。人C4b结合蛋白（C4bp）、膜辅助因子蛋白（MCP）以及Hhu可参与Igp或Ihu对C3(MA)gp的裂解。在这些测定中，C3(MA)gp再次降解的效率低于C3(MA)hu。有趣的是，人C3b/C4b受体（CR1）介导I因子依赖的C3(MA)hu和C3(MA)gp的裂解，且无论I因子的来源如何，程度相似。这些结果表明，除了CR1的情况外，I因子依赖的C3b调节系统具有物种特异性，CR1可能作为一种辅助因子，与物种无关。
