The physiological breakdown of the third component of human complement

Pattern of degradation of human complement fragment, C3b

“…The formation of C3bi described here is in agreement with the findings in [15]. The failure to observe the double cleavage of the a'-chain of C3b in [6,7, 10-14] may be explained by the transient appearance of the 46 000 M r fragment, especially around neutral pH.…”

“…The ~'-chain of C4b is cleaved in two places by C3b/C4b INA [8,9]. However, there is controversy as to whether the a'-chain of C3b is cleaved at a single peptide bond [6,7,[10][11][12][13][14] or in two places [15] by C3b/C4b INA. The product of C3b degradation by/31H and C3b/C4b INA is called C3bi.…”

Optimizing the Identification of Citrullinated Peptides by Mass Spectrometry: Utilizing the Inability of Trypsin to Cleave after Citrullinated Amino Acids

“…The citrullination was found to be on position 1320, the C-terminal aa of the C3f fragment. C3f is a peptide that is released in vivo when C3b is converted to C3ib by the serine protease Factor I during complement activation [28,29]. Therefore, it seems likely that this is an example of the citrullinations that might be missed when implementing the no C-terminal citrullination limitation.…”

Cleavage of C3 by Neutral Proteases from Granulocytes in Pleural Empyema

“…Serum complement is of major importance in the humoral immune response to pyogenic infections, and C3 is currently viewed as the target molecule of both the classical and the alternative pathways of complement activation [1][2][3]. Its acReceived for publication March 10, 1981, and in revised form June 22, 1981.…”

“…Its ac-tivation leads to the production of the biologically active fragment C3b, and the coating of microorganisms with C3b promotes their recognition by PMNLs. Activation proceeds through the cleavage of native C3 by either the classical (C42) or the alternative (C3b, Bb) pathway convertase of C3 or both [2,3]. Recently it has been shown in vitro [4][5][6][7][8] that C3, as well as C5, can be split by complement-unrelated enzymes, such as purified neutral proteases from PMNLs.…”