title: The catalytic chain of human complement subcomponent C1r. Purification and N-terminal amino acid sequences of the major cyanogen bromide-cleavage fragments.
abstract: 1. The a- and b-chains of reduced and alkylated human complement subcomponent C1r were separated by high-pressure gel-permeation chromatography and isolated in good yield and in pure form. 2. CNBr cleavage of C1r b-chain yielded eight major peptides, which were purified by gel filtration and high-pressure reversed-phase chromatography. As determined from the sum of their amino acid compositions, these peptides accounted for a minimum molecular weight of 28 000, close to the value 29 100 calculated from the whole b-chain. 3. N-Terminal sequence determinations of C1r b-chain and its CNBr-cleavage peptides allowed the identification of about two-thirds of the amino acids of C1r b-chain. From our results, and on the basis of homology with other serine proteinases, an alignment of the eight CNBr-cleavage peptides from C1r b-chain is proposed. 4. The residues forming the 'charge-relay' system of the active site of serine proteinases (His-57, Asp-102 and Ser-195 in the chymotrypsinogen numbering) are found in the corresponding regions of C1r b-chain, and the amino acid sequence around these residues has been determined. 5. The N-terminal sequence of C1r b-chain has been extended to residue 60 and reveals that C1r b-chain lacks the 'histidine loop', a disulphide bond that is present in all other known serine proteinases.
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D055598:Chemical Phenomena; D002621:Chemistry; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D003166:Complement Activating Enzymes; D015923:Complement C1r; D003488:Cyanogen Bromide; D006801:Humans; D010446:Peptide Fragments / Q000032:analysis* / Q000302:isolation & purification
chemical_list: D000596:Amino Acids; D010446:Peptide Fragments; D003166:Complement Activating Enzymes; D015923:Complement C1r; D003488:Cyanogen Bromide