Post-translational modification of the fourth component of complement. Sulfation of the α-chain

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The fourth component of complement (C4) was found to incorporate radiolabel from [35S]O4 during synthesis in murine peritoneal macrophages and the human hepatoma-derived cell line, HepG2. The sulfate label was localized to the COOH-terminal autolytic fragment of the C4 α-chain. No label was seen associated with intracellular pro-C4. The structurally similar third and fifth components of complement, and α2-macroglobulin, did not incorporate labeled sulfate. Tryptic peptides from [35S]O4-labeled C4 α-chain were analyzed by reversed phase liquid chromatography and found to elute in a single, homogeneous peak, suggesting a unique sulfation site in the C4 α-chain. Thin layer chromatography of a base hydrolysate of [35S]O4-labeled C4 α-chains, or C4 isolated from human plasma, revealed the presence of tyrosine-O-sulfate. The possible significance of this unusual amino acid modification for the function of C4 is unknown.

Original languageEnglish (US)
Pages (from-to)12745-12748
Number of pages4
JournalJournal of Biological Chemistry
Issue number21
StatePublished - 1983

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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