期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1977
卷号：74
期号：7
页码：2998-3001
DOI：10.1073/pnas.74.7.2998
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The activation of complement component C2 by C[IMG]f1.gif" ALT="1" BORDER="0">[IMG]f2.gif" ALT="s" BORDER="0"> is a major reaction step leading to the assembly of two related macromolecular enzymes in the classical complement pathway C3 convertase and C5 convertase. The present studies clearly document the smaller fragment, C2b, that results when human C2 reacts with C[IMG]f1.gif" ALT="1" BORDER="0">[IMG]f2.gif" ALT="s" BORDER="0">. We have identified and characterized C2b (34,000 daltons) as a single protein on disc electrophoresis and immunoelectrophoresis. C2a (73,000 daltons), the larger fragment from this reaction, has a more acidic nature and C2b is more basic. These fragments can also be detected by their different antigenic determinants. When the C2-C4b complex is activated in the fluid phase by C[IMG]f1.gif" ALT="1" BORDER="0">[IMG]f2.gif" ALT="s" BORDER="0"> and allowed to decay, it dissociates into C2a and the C2b-C4b complex. Furthermore, when C2 is bound to C4b-Sepharose and then reacted with C[IMG]f1.gif" ALT="1" BORDER="0">[IMG]f2.gif" ALT="s" BORDER="0">, only the C2a fragment is released from the solid phase C2-C4b-Sepharose into the fluid phase, and the C2b fragment remains noncovalently bound to C4b-Sepharose. These results suggest that the C2b portion of C2 contains a stable binding site for C4b and, after the decay release of C2a from this C3 convertase, the C2b fragment remains bound. Thus, the decay release of C2a may represent a temperature-dependent dissociation from C2b.
