标题：Identification and partial characterization of the secreted form of the fourth component of human complement: evidence that it is different from major plasma form
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：1983
卷号：80
期号：1
页码：268-272
DOI：10.1073/pnas.80.1.268
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Immunoprecipitation of human C4 from plasma followed by NaDodSO4/polyacrylamide gel electrophoresis under reducing conditions revealed the expected alpha, beta, and gamma chains as well as a smaller quantity of a molecule containing an alpha chain (p98) approximately equal to 5,000 daltons heavier than the normal alpha chain. Further studies on p98 indicated that it covalently incorporated methyl-amine, was present at a concentration of approximately equal to 8% of the principal plasma form of the C4 alpha chain, and was found in highly purified C4 preparations. Hep G2, a human hepatoma-derived cell line, was found to secrete a C4 molecule in which the alpha chain had a molecular weight identical to that of the p98 protein found in plasma. The secreted C4 molecule possessed hemolytic activity. The 5,000-dalton difference in the alpha chain was localized to the COOH terminus and was attributed to an additional polypeptide. We propose that p98 is the alpha chain of the secreted form of C4, which is processed extracellularly by proteolytic cleavage to the principal C4 molecule found in plasma.
