Product Description

Rat C3 is purifiedfrom pooled normal rat serum. C3 is central to the activation of allthreepathways of complement activation (Law, S.K.A. and Reid, K.B.M.(1995)).Initiation of each pathway generates proteolytic enzymecomplexes (C3convertases) which are bound to the target surface. Theseenzymes cleave apeptide bond in C3 releasing the anaphylatoxin C3aand activating C3b. For abrief time (~60 µs) this nascent C3b iscapable of reacting with and covalentlycoupling to hydroxyl groups onthe target surface. Carbohydrates are thefavored target, but proteinhydroxyls and amino groups also react. This processof tagging thetarget surface with C3b is called opsonization. The reactivesite innascent C3b is a thioester (Tack B.J., et al. (1980); Pangburn M.K. and MüllerEberhard H.J. (1980)) and C3b is linked to the target through acovalentester bond (an amide bond is formed if C3b is attached toamino groups). Mostof the C3 activated during complement activationnever attaches to the surfacebecause its thioester reacts with waterforming fluid phase C3b which israpidly inactivated by factors H and Iforming iC3b. Surface-bound C3b isnecessary in all three pathways forefficient activation of C5 and formation ofC5b-9 complexes that lysethe target cell membrane. Surface-bound C3b and itsbreakdown productsiC3b and C3d are recognized by numerous receptors onlymphoid andphagocytic cells which use the C3b ligand to stimulate antigen presentation to cells of the adaptive immune system. The end result isanexpansion of target-specific B-cell and T-cell populations.

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