Freeze-thaw activation of the complement attack phase: I. Separation of two steps in the formation of the active C--56 complex.
The activation of the attack phase of C, C5-C9, is generally assumed to be dependent on the enzymes of the C activation pathways which cleave C5 into C5b and C5a. C5b will then form a complex with C6 that binds to membranes and, in the presence of C7-C9, effects cell lysis. In contrast, however, a variety of physicochemical means was found to activate C5 + C6 independently of the convertases and without apparent generation of the C5a peptide. By freezing and thawing of C5 + C6 a hemolytic C--56 activity was generated: (C--56 ).f The activation proceeded in two steps: (1) during a preincubation period of the two components the time and temperature dependent formation of an activatable intermediate was observed and (2) the intermediate C--56 could then be endowed with hemolytic activity by freezing and thawing. The intermediate as well as the activated (C--56)f complex was separated from C5 and C6 by anion exchange chromatography. While the isolated intermediate was labile, the active product after freezing and thawing was stable.
D003167:Complement Activation; D003182:Complement C5 / Q000378:metabolism*; D003183:Complement C6 / Q000378:metabolism*; D015938:Complement Membrane Attack Complex; D003165:Complement System Proteins / Q000378:metabolism; D005615:Freezing; D006460:Hemolysin Proteins / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques
D003182:Complement C5; D003183:Complement C6; D015938:Complement Membrane Attack Complex; D006460:Hemolysin Proteins; D003165:Complement System Proteins