C 1 Esterase

A 77-kDa subcomponent of Complement C1, encoded by Gene C1S, is a Serine Protease existing as a proenzyme (homodimer) in the intact Complement C1 complex. Upon the binding of Complement C1q to Antibodies, the activated Complement C1r cleaves C1s into two chains, A (heavy) and B (Light, the Serine Protease), linked by disulfide bonds yielding the active C1s. The activated C1s, in turn, cleaves Complement C2 and Complement C4 to form C4b2a (Classical C3 Convertase).