Mori Y, Ueda E, Takeuchi T, Taniuchi S, Koyama J
J Biochem. 1980 Jun;87(6):1757-63. doi: 10.1093/oxfordjournals.jbchem.a132920.
When rabbit C1 purified by affinity chromatography on IgG-Sepharose 6B was chromatographed on DEAE-cellulose in the presence of ethylenediaminetetraacetate, C1s was isolated as two forms, C1s(I) and C1s(II), having different molecular weights. On the other hand, incubation of the C1 with soybean trypsin inhibitor before the chromatography resulted in the isolation of C1s(I) alone, indicating that, during the purification, C1s(II) was derived from C1s(I) by proteolytic cleavage of C1s(I) by a contaminating protease, probably plasmin [EC 3.4.21.7]. In fact, C1s(I) was completely converted to C1s(II) or a C1s(II)-like fragment by highly purified plasmin. Analysis of the polypeptide chain structures revealed that C1s(I), which consisted of H and L chains with molecular weights of 70,000 and 36,000, respectively, was converted to C1s(II) by cleavage of the H chain, since C1s(II) consisted of two chains each with a molecular weight of 37,000. This conversion proceeded without any alteration in C1 esterase activity, but was accompanied by loss of the ability to form C1r-C1s complex.
当通过在IgG-Sepharose 6B上进行亲和层析纯化的兔C1在乙二胺四乙酸存在下于DEAE-纤维素上进行层析时，C1s被分离为两种形式，即具有不同分子量的C1s(I)和C1s(II)。另一方面，在层析前用大豆胰蛋白酶抑制剂孵育C1，结果仅分离出C1s(I)，这表明在纯化过程中，C1s(II)是由污染的蛋白酶（可能是纤溶酶[EC 3.4.21.7]）对C1s(I)进行蛋白水解切割而从C1s(I)衍生而来的。事实上，高度纯化的纤溶酶可将C1s(I)完全转化为C1s(II)或类似C1s(II)的片段。对多肽链结构的分析表明，由分子量分别为70,000和36,000的重链和轻链组成的C1s(I)，通过重链的切割转化为C1s(II)，因为C1s(II)由两条分子量均为37,000的链组成。这种转化在C1酯酶活性没有任何改变的情况下进行，但伴随着形成C1r-C1s复合物能力的丧失。
