Bioscience Reports

, Volume 1, Issue 6, pp 461–468 | Cite as

Intramolecular general acid catalysis in the binding reactions of α2 and complement components C3 and C4

  • Stephen G. Davies
  • Robert B. Sim


The complement system proteins C3 and C4 and the plasma protease inhibitor α2-macroglobulin~ when activated by limited proteolysis, can bind covalently to other macromolecules. The three proteins also exhibit an unusual internal peptide-bond cleavage reaction when denatured. The covalent binding reaction is likely to occur by a transacylation mechanism involving an internal thioiester in the three proteins. However, the activated species of these proteins are much more reactive than simple thiolesters. Studies of molecular models of the thiolester region in C3 show that an intramolecular acid catalysis mechanism can both account for the exceptional reactivity of the activated form of these proteins and provide an explanation for the denaturation-induced peptide bond cleavage.


Macromolecule Bond Cleavage Peptide Bond Complement System Complement Component 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© The Biochemical Society 1981

Authors and Affiliations

  • Stephen G. Davies
    • 1
  • Robert B. Sim
    • 2
  1. 1.The Dyson Perrins LaboratoryOxfordUK
  2. 2.MRC Immunochemistry Unit, Department of BiochemistryUniversity of OxfordOxfordUK

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