Sim R B
Biochem J. 1985 Dec 15;232(3):883-9. doi: 10.1042/bj2320883.
A large-scale procedure for the isolation of complement receptor type 1 (CR1, the C3b receptor) from human erythrocytes is described. Two of the four known phenotypes of CR1 are detectable in the isolated material. Amino acid and hexosamine analysis of the A phenotype (Mr 240 000) indicates a polypeptide chain length of about 2030 amino acids and a carbohydrate content of 8%. Both N- and O-linked sugars appear to be present. Trypsin digestion of isolated CR1 shows that it is degraded rapidly and extensively, and no stable products of Mr greater than 25000 are found. The ability of the receptor to bind to solid-phase ligand is destroyed after a single cleavage by trypsin. The capacity of the receptor to act as a cofactor for Factor I-mediated cleavage of soluble C3b is, however, only gradually decreased by proteolysis, and 30% of this activity remains after extensive degradation. The same pattern of loss of binding to solid-phase ligand, with partial retention of interaction with soluble ligand, is also characteristic of the complement proteins Factor H and C4bp, which are functionally related to CR1.
本文描述了一种从人红细胞中分离补体受体1型（CR1，即C3b受体）的大规模方法。在分离出的物质中可检测到CR1四种已知表型中的两种。对A表型（分子量240 000）进行氨基酸和己糖胺分析表明，其多肽链长度约为2030个氨基酸，碳水化合物含量为8%。N-连接糖和O-连接糖似乎都存在。对分离出的CR1进行胰蛋白酶消化显示，它迅速且大量地被降解，未发现分子量大于25000的稳定产物。受体与固相配体结合的能力在被胰蛋白酶单次切割后即被破坏。然而，受体作为I因子介导的可溶性C3b裂解辅因子的能力仅因蛋白水解而逐渐降低，在广泛降解后仍保留30%的这种活性。与固相配体结合能力丧失，而与可溶性配体相互作用部分保留的相同模式，也是与CR1功能相关的补体蛋白H因子和C4bp的特征。
