C1q, together with C1r and C1s, in the ratio of 1:2:2, form the C1 complex which is the first component of the classical complement pathway. It is composed of 18 polypeptide chains (six A, six B, six C). All contain an 81 amino acid collagen like region composed of (Gly-Xaa-Yaa) repeating sequences close to the N-terminus. Three chains (A1B1C1) form a triple helix with the C-terminus forming the globular heads which may be structurally and functionally distinct domains.

• Supplied in HEPES, 40% glycerol

It is an important regulator factor for platelet activation. It plays an important role in inflammatory conditions such as coronary heart disease. It has been shown to inhibit collagen induced aggregation and enhance production of reactive oxygen species (ROS).