Also Mg2+ ions are necessary for forming a functional C3 convertase.

Catalytic site of C3 convertase is in C2a and Bb subunits.

Term C3 convertase may refer to:

Another form, the classical pathway C3 convertase contains different proteins of complement system - C4b and C2a.

Thus, the alternative pathway C3 convertase is formed and is able to cleave C3 now.

Bb will remain associated with C3b to form C3bBb, which is the alternative pathway C3 convertase.

Decay-accelerating factor (DAF) is another negative regulator of C3 convertase.

The resultant complex, C3bBb, is called the alternative pathway (AP) C3 convertase.

C4 binding protein (C4-bp) interferes with the assembly of the membrane-bound C3 convertase of the classical pathway.

After the creation of C3 convertase, the complement system follows the same path regardless of the means of activation (alternative, classical, or lectin).

C3 convertase is, in classical terms, C4b2a; in the 1990s there was a motion put forward to change the nomenclature to C4b2b, however this was unsuccessful.

The formation of a C3 convertase can also be prevented when a plasma protease called complement factor I cleaves C3b into its inactive form, iC3b.

All pathways culminate in the production of a C3 convertase, which catalyses C3 into its constitutive parts (better detailed here - classical complement pathway).

C3 convertase exists in two forms (C3bBb and C4bC2a) but both of them cleave only C3, central molecule of complement system.

C3 convertase cleaves C3 producing C3b which can form an additional C3 convertase.

DAF acts on C2a and Bb and dissociates them rapidly from C4b and C3b - thereby preventing the assembly of the C3 convertase.

Once the alternative C3 convertase enzyme is formed on a pathogen or cell surface, it may bind covalently another C3b, to form C3bBbC3bP, the C5 convertase.

It exerts antibacterial effects by depriving bacteria of iron required for growth, and it has anti-inflammatory poperties - for example, by preventing complement activation through inhibition of classical C3 convertase.

C4 binding protein and C3b inactivator control the C3 convertase of the classical pathway in a similar way to that described for β1H and C3b inactivator in the alternative pathway.

The C3bBb complex is stabilized by binding oligomers of factor P. The stabilized C3 convertase, C3bBbP, then acts enzymatically to cleave much more C3, some of which becomes covalently attached to the same surface as C3b.

The classical pathway C5 convertase is composed of the larger fragments of complement proteins, C4b, C2a produced by cleavage mediated by C1 complex, and C3b produced by cleavage mediated by the classical pathway C3 convertase (C4bC2a).

C3b that is generated from C3 by a C3 convertase enzyme complex in the fluid phase is rapidly inactivated by factor H and factor I, as is the C3b-like C3 that is the product of spontaneous cleavage of the internal thioester.

Complement Factor H can inhibit the formation of the C3 convertase by competing with factor B for binding to C3b; accelerate the decay of the C3 convertase; and act as a cofactor for Factor I-mediated cleavage of C3b.

C4b2a is able to catalyse the assembly of the C3-convertase.

This complex is also known as a fluid-phase C3-convertase.

C4b forms part of C3-convertase, in conjunction with 2a:

C4b and C2b then bind together to form C3-convertase, as in the classical pathway.

This leads to the production of surface-bound C3-convertase and thus more C3b components.

The C4b fragments can then bind to the surface of the bacterium, and initiate the formation of a C3-convertase.

The three pathways of activation all generate homologous variants of the protease C3-convertase.

C1s cleaves C4, which eventually leads to the production of the C4b-C2a form of C3-convertase.

C3 Nephritic Factor stabilizes C3-convertase, leading to Hypocomplementemia.

Binding of another C3b-fragment to the C3-convertase of the alternative pathway creates a C5-convertase analoguous to the lectin or classical pathway.

Once formed, both C3 convertases will catalyze the proteolytic cleavage of C3 into C3a and C3b (hence the name "C3-convertase").

The alternative pathway C3-convertase consists of the activated B and C3b factors, forming an unstable compound that can become stable after binding properdin, a serum protein.

MASP-1 is involved in the lectin pathway of the complement system and is responsible for cleaving C4 and C2 to form C4b2a, a C3-convertase.

C4BP accelerates decay of C3-convertase and is a cofactor for serine protease factor I which cleaves C4b and C3b.

C3-convertase can be inhibited by Decay accelerating factor (DAF), which is bound to erythrocyte plasma membranes via a GPI anchor.

In the alternative complement pathway, C3 is cleaved by C3bBb, another form of C3-convertase composed of activated forms of C3 (C3b) and factor B (Bb).

It prevents the assembly of the C3bBb complex (the C3-convertase of the alternative pathway) or accelerates the disassembly of preformed convertase, thus blocking the formation of the membrane attack complex.

Factor H regulates complement activation on self cells and surfaces by possessing both cofactor activity for the Factor I mediated C3b cleavage, and decay accelerating activity against the alternative pathway C3-convertase, C3bBb.