Product Description

Rat C3b is derived from native purified rat C3 (CompTech#M113) uponcleavage and release of C3a with the alternative pathway C3 convertase. C3 is central to the activation of all three pathways ofcomplementactivation (Law, S.K.A. and Reid, K.B.M. (1995)). Initiationof each pathwaygenerates proteolytic enzyme complexes (C3convertases) which are bound to thetarget surface. These enzymescleave a peptide bond in C3 releasing theanaphylatoxin C3a andactivating C3b. For a brief time (~60 µs) this nascentC3b is capableof reacting with and covalently coupling to hydroxyl groups onthetarget surface. Carbohydrates are the favored target, but proteinhydroxylsand amino groups also react. This process of tagging thetarget surface withC3b is called opsonization. The reactive site innascent C3b is a thioester(Tack B.J., et al. (1980); Pangburn M.K. andMüllerEberhard H.J. (1980)) andC3b is linked to the target through acovalent ester bond (an amide bond isformed if C3b is attached toamino groups). Most of the C3 activated duringcomplement activationnever attaches to the surface because its thioesterreacts with waterforming fluid phase C3b which is rapidly inactivated byfactors H and Iforming iC3b. Surface-bound C3b is necessary in all three pathwaysforefficient activation of C5 and formation of C5b-9 complexes that lysethetarget cell membrane. Surface-bound C3b and its breakdown productsiC3b and C3dare recognized by numerous receptors on lymphoid andphagocytic cells which usethe C3b ligand to stimulate antigenpresentation to cells of the adaptiveimmune system. The end result isan expansion of target-specific B-cell andT-cell populations.

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Complement Technology的C1是级联反应中的第一个补体成分，称为补体经典途径。C1与抗原结合的抗体（免疫复合物）结合并被其激活，从而产生引发级联反应的蛋白酶。C1实际上是钙依赖性复合物中结合在一起的三种不同蛋白质（C1q，C1r和C1s）的非共价复合物。C1q通过其六个臂中的两个或多个与IgG或IgM的Fc结构域结合。多臂与免疫复合物的结合被认为会引入压力，从而导致复合物中的两个C1r蛋白（蛋白酶酶原）自身激活，从而产生两种活性的C1r丝氨酸蛋白酶（Morikis，D.和Lambris，JD（2005））。 。这些激活的C1r亚基裂解并激活复合物中的两个C1s蛋白酶酶原。活化的C1裂解补体成分C4，释放出C4a，并启动C4b与活化表面的共价连接。活化的C1也切割C2，并且C2的较大片段结合至表面附着的C4b，形成C4b，C2a，其为经典途径的C3 / C5转化酶。