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补体第四成份(C4)是一种多功能蛋白质,对经典途径C3转化酶的形成起关键作用。C4分子由α、β及γ三链组成,其间连以二硫键,但合成时是一单链前体分子。人C4是由第6号染色体主要组织相容性复合体进行遗传编码,表现多态现象。近来证实,C4的不同型式不是单一座位的共显性等位基因,而是由两个紧密连锁的等位基因所编码,某些人C4可表现四种结构形式。这一蛋白的电泳表现可分为两组:酸性的C4A及碱性的C4B,并证明与红细胞抗原Rodgers及Chido蜜切相关。C4A为Rg~+、Ch~-,C4B为Rg~-、Ch~+。先已证实,Ch 与Rg的抗原决定簇位于C4d区,后来发现C4A与C4B两个同种型的差别也在于C4d区。
The fourth component of complement (C4) is a multifunctional protein that plays a key role in the formation of the classical pathway C3 convertase. The C4 molecule consists of alpha, beta and gamma triple strands with a disulfide bond in between, but synthesizes a single-stranded precursor molecule. Human C4 is encoded by the major histocompatibility complex on chromosome 6, showing polymorphism. It has recently been demonstrated that the different versions of C4 are not codominant alleles for a single locus but rather are encoded by two closely linked alleles, some of which exhibit four structural forms. The electrophoretic performance of this protein can be divided into two groups: acidic C4A and basic C4B, and proved to be associated with the erythrocyte antigen Rodgers and Chido honey. C4A is Rg ~ +, Ch ~ -, C4B is Rg ~ -, Ch ~ +. It has been confirmed that Ch and Rg epitopes located in the C4d region, and later found C4A and C4B two isoforms also lies in the C4d region.