Law S K
Biochem J. 1983 May 1;211(2):381-9. doi: 10.1042/bj2110381.
The covalent binding of [3H]glycerol to C3 by the transfer of the acyl group of the internal thioester of C3 to the hydroxy group of glycerol can be activated either proteolytically by trypsin or by various chaotropes and denaturants. The activation of binding by trypsin or KBr showed similar dependence on the concentration of glycerol, indicating a similar activation mechanism. It is therefore concluded that the conformational change of the protein is the critical step in the binding reaction, and that the conversion of C3 into C3b under physiological conditions is only a means to induce the conformational change. Guanidinium chloride induces the binding of glycerol to C3 at concentrations of about 1 M. On increasing the concentration of guanidinium chloride the extent of binding declines and is accompanied by an increase in the autolytic cleavage reaction [Sim & Sim (1981) Biochem. J. 193, 129-141]. The autolytic cleavage reaction is therefore not independently activated with respect to the binding reaction. Its occurrence, however, is structurally restricted under physiological or limited denaturing conditions and is permissible only when C3 is brought to a higher denaturation state.
通过将C3内部硫酯的酰基转移至甘油的羟基上，[3H]甘油与C3的共价结合可通过胰蛋白酶进行蛋白水解激活，也可被各种离液剂和变性剂激活。胰蛋白酶或KBr对结合的激活表现出对甘油浓度的相似依赖性，表明激活机制相似。因此可以得出结论，蛋白质的构象变化是结合反应中的关键步骤，并且在生理条件下C3转化为C3b只是诱导构象变化的一种方式。在约1 M的浓度下，氯化胍可诱导甘油与C3的结合。随着氯化胍浓度的增加，结合程度下降，并伴随着自溶裂解反应的增加[Sim & Sim(1981) Biochem. J. 193, 129 - 141]。因此，自溶裂解反应相对于结合反应并非独立激活。然而，其发生在生理或有限变性条件下受到结构限制，并且只有当C3处于更高的变性状态时才会发生。
