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：1975
卷号：72
期号：8
页码：3220-3224
DOI：10.1073/pnas.72.8.3220
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Activation of the classical complement (C) system involves conversion of C1 to its active state with subsequent cleavage of C4 and -d C2 so as to form the classical C3 convertase, C42 (a bar indicates the activated form of a protein), which sequentially cleaves C3 and C5 to initiate the cytolytic event associated with the complete reaction. An alternative, pr properdin-dependent, pathway to complement activation generates a C3 convertase, C3B, that is formed by cleavage of B with D in the presence of a C3b, the major cleavage fragment of C3. C3b is capable of binding activated properidin (P) with resultant stabilization of C3B, which otherwise rapidly decays by loss of B activity. Initial cleavage of C3, a prerequisite for formation of C3B, is demonstrated to occur through the interaction of native C3 and B in the presence of either D or P alone, or together. The effect of P on the interaction of D, B, and C3 is attributed to stabilization of C3B as has been shown for C3B. Larger amounts of P and B with C3 in the absence of D form a C3 convertase that is designated (P)C3B to indicate that demonstrable cleavage of B does not occur although the active site is available. The generation of this initial convertase, as assessed by C3 inactivation, is dose-related to P and B inputs. The presence of both P and D greatly augments initial cleavage of C3 with D fully uncovering the active site of B and P stabilizing that site.
