Autolytic fragmentation of complement components C3 and C4 under denaturing conditions, a property shared with XXXX .

@entity5843 @entity1133 @entity9199 @entity4417 @entity8696 @entity2097 @entity2975 @entity214
The alpha polypeptide chain of the complement protein C3 splits into two fragments of 74 000 and 46 000 apparent mol.wt. under certain conditions used to prepare the protein for @entity214 ( @entity214 )/ @entity2975 -gel electrophoresis. The cleavage reaction occurs over a wide range of temperatures and from pH 4.6 to 10.6 in the presence of denaturants such as @entity1133 , @entity214 and @entity2097 . It is also induced by heat-denaturation of C3 in the absence of chemical denaturants. The reaction occurs only with haemolytically active C3, and is not observed with @entity8696 -inactivated C3 or with @entity4417 . A similar cleavage of the alpha-chain of complement component C4 occurs under the same conditions, forming fragments of 53 000 and 41 000 apparent mol.wt. This reaction is again specific for haemolytically active C4, and does not occur with @entity9199 or @entity8696 -inactivated C4. The complement component C5, although structurally similar to C3 and C4, does not undergo a reaction of this type. The characteristics of the denaturation-induced cleavage of C3 and C4 match those described for the 'heat-induced' cleavage of @entity5843 [Harpel, Hayes _ Hugli (1979) J. Biol. Chem. 254, 8669-8678]. Cleavage of @entity5843 is also specific for the active form of the protein, and does not occur with chemically inactivated or proteinase-cleaved forms. The unusual conditions and specificity of the peptide-bond cleavage in all three proteins suggest that it is an autolytic process rather than being the result of trace proteinase contamination. The active forms of C3, C4 and @entity5843 have the transient ability to form covalent bonds after activation. The autolytic cleavage reaction is likely to be related to the covalent-bond-forming reactions of these proteins.
