Native Human C8 Protein

Cat.No.: C8-103H
Description: Native human C8 is a naturally glycosylated protein composed of three polypeptide chains. The total molecular weight is 151,000 Da. The alpha chain (64,000 Da) and the gamma chain (22,000 Da) are disulfide linked. The beta chain (64,000 Da) is non-covalently bound to the a-g complex. C8 is essential for formation of the membrane attack complex (MAC) and is activated non-proteolytically by binding to newly-formed C5b,C6,C7 complexes on the cell membrane. Each pathway of complement activation generates proteolytic enzyme complexes (C3/C5 convertases) which are bound to the target surface (Ross, G.D. (1986)). These enzymes cleave a peptide bond in the larger alpha chain of C5 releasing the anaphylatoxin C5a and activating C5b. This is the only proteolytic step in the assembly of the C5b-9 complex. C5b is unstable, but it remains bound to the activating complex for a brief time (~2 min) during which it either binds a single C6 from the surrounding fluid or decays and is no longer capable of forming MAC. The C5b,6 complex may also remain bound to the C3/C5 convertase where the binding of a single C7 exposes a membrane-binding region and C5b,6,7 can partially insert into the bilipid layer of the target cell. Up to this point the complex may diffuse away from the target cell and enter the membrane of a nearby cell. This is called bystander lysis or "reactive lysis" and can be a significant source of pathology. Each C5b-7 complex can bind one C8 protein molecule which results in the complex inserting more firmly into the membrane. The C5b-8 complex is capable of causing lysis without C9 although this is slow and requires many more complexes per cell than with C9. This property complicates C9 titrations since the precursor (C5b-8) can also cause lysis. The primary role of C8 is to catalyze the binding of C9 and each bound C9 can bind another C9 initiating formation of a ring structure containing up to 18 molecules of C9 (Podack, E.R. (1984)). C5b-9 complexes with one or more C9 are referred to as the Membrane Attack Complex (MAC) of complement. Not all C5b-8 complexes have complete rings of C9 with the average being only three C9 per C5b-8 complex.
Source: Normal human serum (shown by certified tests to be negative for HBsAg, HTLV-I/II, STS and for antibodies to HCV, HIV-1 and HIV-II).
Species: Human
Form: Liquid
Molecular Mass: 151,000 Da (3 chains)
Purity: >90% by SDS-PAGE
Characteristic: The molecular weight of C8 is 151,000 Da and it is composed of three polypeptide chains. The alpha chain (64,000 Da) and the gamma chain (22,000 Da) are disulfide linked. The beta chain (64,000 Da) is non-covalently bound to the a-g complex. The pI of C8 is heterogeneous from 6.2 to 7.5.
Usage: For research use only. Not for human or drug use.
Storage: -70°C or below. Avoid freeze/thaw.
Concentration: 1.0 mg/mL (see Certificate of Analysis for actual concentration)
Storage Buffer: 10 mM Sodium phosphate, 145 mM NaCl, pH 7.3
Preservative: None, 0.22 μm filtered
Warning: Use normal precautions for handling human blood products.

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