Freeze-thaw activation of the complement attack phase: II. Comparison of convertase generated C--56 with C--56 generated by freezing and thawing.
The activation of the C-attack phase does not necessarily involve the components of the C5 convertases. C--56 hemolytic activity was generated from the same source of C7 depleted serum by the alternative pathway convertase or by freezing and thawing resp. In contrast to activation by the convertase, biological activities of C5a (chemotaxis, serotonin release) were not detected following activation by freezing. The yields of C--56 hemolytic activities were similar and the properties of the activated products were identical. No difference was found in the molecular weight, in the hydrophobicity or with respect to charge. The two activities were in the absence of C7 stable at 37 degrees C and decayed rapidly in the presence of C7. It is proposed that a conformational change in the tertiary structure of the molecule(s) is the critical event in the formation of an active C--56 complex. In this light the cleavage of C5a from the native molecule by the convertase appears as a side reaction, not by itself essential for activation.
D003166:Complement Activating Enzymes / Q000378:metabolism; D003167:Complement Activation; D050577:Complement C3-C5 Convertases; D003182:Complement C5 / Q000378:metabolism*; D015936:Complement C5a; D003183:Complement C6 / Q000378:metabolism*; D003184:Complement C7 / Q000378:metabolism; D015938:Complement Membrane Attack Complex; D003165:Complement System Proteins / Q000378:metabolism; D005615:Freezing; D006801:Humans; D066298:In Vitro Techniques; D008970:Molecular Weight; D011487:Protein Conformation
D003182:Complement C5; D003183:Complement C6; D003184:Complement C7; D015938:Complement Membrane Attack Complex; D015936:Complement C5a; D003165:Complement System Proteins; D003166:Complement Activating Enzymes; D050577:Complement C3-C5 Convertases