A 80-kDa subcomponent of complement C1, existing as a SERINE PROTEASE proenzyme in the intact complement C1 complex. When COMPLEMENT C1Q is bound to antibodies, the changed tertiary structure causes autolytic activation of complement C1r which is cleaved into two chains, A (heavy) and B (light, the serine protease), connected by disulfide bonds. The activated C1r serine protease, in turn, activates COMPLEMENT C1S proenzyme by cleaving the Arg426-Ile427 bond. No fragment is released when either C1r or C1s is cleaved.

DUI

D015923 MeSH Browser

CUI

M0024367

Previous indexing

Complement Activating Enzymes (1979-1989); Complement 1 (1979-1989); Enzyme Precursors (1979-1982)

History note

2006 (1990)

Public note

2006; see COMPLEMENT 1R 1990-2005