title: Clr and Cls subcomponents of human complement: two serine proteinases lacking the 'histidine-loop' disulphide bridge.
abstract: The N-terminal amino acid sequence of human C1s b chain has been extended to 52 residues. The histidine residue involved in the charge-relay system is located at position 38, whereas the histidine-loop disulphide bridge is missing. So far, human complement sub-components C1r and C1s are the only known mammalian serine proteinases lacking this disulphide bridge.
mesh_terms: D000595:Amino Acid Sequence; D055598:Chemical Phenomena; D002621:Chemistry; D003166:Complement Activating Enzymes / Q000302:isolation & purification; D015923:Complement C1r; D003173:Complement C1s; D004220:Disulfides / Q000378:metabolism*; D010450:Endopeptidases; D006639:Histidine; D006801:Humans; D012697:Serine Endopeptidases; D013329:Structure-Activity Relationship
chemical_list: D004220:Disulfides; D006639:Histidine; D003166:Complement Activating Enzymes; D010450:Endopeptidases; D012697:Serine Endopeptidases; D015923:Complement C1r; D003173:Complement C1s