title: Structure and activation of complement components C2 and factor B.
abstract: The activation of complement is initiated by two independent pathways. Each leads to the formation of a complex protease, C3 convertase, with equivalent specificity and function but different composition. The convertase derived from the classical pathway is composed of complement components C4 and C2 while that from the alternative pathway consists of components C3 and Factor B. C2 and Factor B contain the catalytic site of each convertase respectively. The amino acid sequence of Factor B has been determined. Limited sequence of CNBr-peptides isolated from C2 has also been obtained. The two enzymes are shown to be homologous and to represent a novel type of serine proteinase, characterized by their unusual structure and mechanism of activation, when compared to known serine proteinases.
mesh_terms: D000595:Amino Acid Sequence; D003175:Complement C2 / Q000378:metabolism*; D050577:Complement C3-C5 Convertases / Q000378:metabolism; D011415:Complement Factor B / Q000378:metabolism*; D003488:Cyanogen Bromide; D010450:Endopeptidases / Q000378:metabolism; D004792:Enzyme Precursors / Q000378:metabolism*; D006801:Humans; D008970:Molecular Weight; D010446:Peptide Fragments / Q000032:analysis; D012697:Serine Endopeptidases
chemical_list: D003175:Complement C2; D004792:Enzyme Precursors; D010446:Peptide Fragments; D010450:Endopeptidases; D050577:Complement C3-C5 Convertases; D012697:Serine Endopeptidases; D011415:Complement Factor B; D003488:Cyanogen Bromide