Seya T, Okada M, Hazeki K, Nagasawa S
Department of Immunology, Center for Adult Diseases, Osaka, Japan.
Biochem Biophys Res Commun. 1990 Jul 31;170(2):504-12. doi: 10.1016/0006-291x(90)92120-o.
Complement factor I is a plasma protease serving for proteolytic inactivation of C3b together with its cofactor. We have identified two factor I-cofactor activities in solubilized extracts of guinea-pig peritoneal granulocytes using guinea-pig factor I (Igp) and fluorescent-labeled methylamine-treated guinea-pig C3 (f-C3(MA)gp). One of these eluted from a chromatofocusing column between pH 7.6-7.1, and the other at about pH 5.7. These two cofactor fractions both interacted with Igp and, to a lesser degree, with human factor I (Ihu) on C3(MA)gp cleaving it into an inactive C3bi analogue, but did not cleave methylamine-treated human C3 (C3(MA)hu) together with Igp or Ihu. These factors are therefore species specific. The neutral and acidic fractions with cofactor activity contained C3(MA)gp-binding proteins with a doublet of 55 kDa and 42 kDa, and a singlet of 160 kDa, respectively, on SDS-PAGE. These proteins may be membrane cofactor protein (MCP) and C3b/C4b receptor (CR1) of guinea-pigs.
补体因子I是一种血浆蛋白酶，可与其辅因子一起对C3b进行蛋白水解失活。我们使用豚鼠因子I（Igp）和荧光标记的甲胺处理的豚鼠C3（f-C3(MA)gp），在豚鼠腹膜粒细胞的可溶性提取物中鉴定出两种因子I-辅因子活性。其中一种从色谱聚焦柱在pH 7.6 - 7.1之间洗脱，另一种在约pH 5.7处洗脱。这两个辅因子组分都与Igp相互作用，并且在较小程度上与人类因子I（Ihu）相互作用，在C3(MA)gp上使其裂解为无活性的C3bi类似物，但不会与Igp或Ihu一起裂解甲胺处理的人类C3（C3(MA)hu）。因此，这些因子具有物种特异性。具有辅因子活性的中性和酸性组分在SDS-PAGE上分别含有与55 kDa和42 kDa的双峰以及160 kDa的单峰结合的C3(MA)gp结合蛋白。这些蛋白质可能是豚鼠的膜辅因子蛋白（MCP）和C3b/C4b受体（CR1）。
