C1 is controlled by?

The initial enzyme, Cl, is a complex formed through a calcium-dependent association between two reversibly interacting subunits, Clq and Clr2s2. In the absence of an immune response, approximately 70% of Cl exists as a complex between these two subunits. Cl occurs in serum as a proenzyme that tends to undergo autoactivation (in which the two subunits are bound together) but is strictly controlled by Cl-inhibitor (Cl-In or Cl esterase).