title: The complement component C1s catalysed hydrolysis of peptide 4-nitroanilide substrates.
abstract: The kinetic parameter kcat/Km has been determined for the hydrolysis of peptide 4-nitroanilides, catalysed by complement component C1s. Substrates based on the C-terminal sequence of human C4a (Leu-Gln-Arg) were synthesised. Replacement of the glutamine residue by glycine or serine increased kcat/Km. Substitution of valine for the leucine residue increased kcat/Km, while substitution of glycine or lysine for the leucine residue decreased kcat/Km slightly. D-Val-Ser-Arg 4-nitroanilide is the most reactive 4-nitroanilide substrate towards C1s, so far. These results are discussed in relation to the amino acid sequences near the bonds cleaved by C1s in C4, C2 and C1 inhibitor.
mesh_terms: D000595:Amino Acid Sequence; D000814:Aniline Compounds / Q000378:metabolism*; D003166:Complement Activating Enzymes / Q000378:metabolism*; D003172:Complement C1 / Q000378:metabolism*; D003173:Complement C1s; D006868:Hydrolysis; D007700:Kinetics; D013379:Substrate Specificity
chemical_list: D000814:Aniline Compounds; D003172:Complement C1; C019498:4-nitroaniline; D003166:Complement Activating Enzymes; D003173:Complement C1s