Reevaluation of total, free, and bound protein S and C4b-binding protein levels in plasma anticoagulated with citrate or hirudin

John H. Griffin, András Gruber, José A. Fernández

Research output: Contribution to journalArticlepeer-review

130 Scopus citations


The levels of total, free, and bound protein S and C4BP were determined using enzyme-linked immunosorbent assays (ELISAs) in plasma samples (8 males and 8 females) that were individually subjected to immunoadsorption studies in which "free protein S" was defined as that not adsorbed by anti-C4BP antibody-Sepharose column and "free C4BP" as that not adsorbed by anti-protein S antibody-Sepharose. Bound species were calculated as the difference between total and free species. Free protein S (131 nmol/L) averaged 38% of total protein S (346 nmol/L) and free C4BP (37 nmol/L) averaged 14% of total C4BP (264 nmol/L) in plasma. There was an excellent correlation between bound protein S and bound C4BP with 1:1 molar stoichiometry and a good correlation between free protein S antigen and protein S anticoagulant activity. It appears that free protein S is a necessary consequence of the molar excess of protein S over C4BP. C4BP β chain antigen levels, measured using a new ELISA, averaged 218 nmol/L, a value indistinguishable from the molar concentrations of bound protein S (215 nmol/L) and bound C4BP (227 nmol/L). The free C4BP β chain antigen was only 4 nmol/L compared with 131 nmol/L free protein S. These results suggest that free C4BP in plasma predominantly lacks the β chain, that almost all C4BP capable of binding protein S is associated with protein S, and that the plasma levels of oligomeric forms of C4BP containing a β chain (α7β and α6β) that bind protein S directly and stoichiometrically regulate free protein S levels.

Original languageEnglish (US)
Pages (from-to)3203-3211
Number of pages9
Issue number12
StatePublished - Jun 15 1992
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Immunology
  • Hematology
  • Cell Biology


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