Fig. 3A: Cleavage of C2 by C1 during
the Classical Complement Pathway - Step 1
C2 binds to the C4b and the enzyme C1 subsequently cleaves C2 into C2a and C2b. The C4b2a functions as a C3 convertase that can enzymatically cleave hundreds of molecules of C3 into C3a and C3b.