# C3 Convertase The C3 convertase cleaves C3 into C3a and C3b. It can be made up of different proteins depending on which complement activation pathway was initiated. ![[Types of C3 Convertase.png|400]] C1 and MBL both cleave C4 and C2 to form C4bC2a. C4bC2a has a different protease specificity and cleaves C3. Although known as the classical C3 convertase, C4bC2a is a component of both the classical and lectin pathways of complement activation, and its formation marks the step where the two pathways converge. The C3 convertase cleaves C3 into C3a, an anaphylatoxin, and C3b, which opsonizes microbial surfaces to mark them for phagocytosis. C3b also combines with C3 convertases to form a C5 convertase. C5b then serves as the anchor point for the membrane attack complex. ![[C3 Convertase.png]]