High molecular weight complex in human plasma between vitamin K-dependent protein S and complement component C4b-binding protein.
Protein S, a recently described vitamin K-dependent plasma protein, is shown to exist in two forms in plasma--free protein and in complex with C4b-binding protein. C4b-binding protein is involved in the regulation of the rate of complement activation. A major proportion of C4b-binding protein in plasma is in complex with protein S. The complex is a major and previously unrecognized component of the group of plasma proteins that adsorbs to barium citrate. The complex dissociates in the presence of NaDodSO4, indicating that C4b-binding protein and protein S are held together by noncovalent bonds. Uncomplexed C4b-binding protein was purified from the supernatant after barium citrate adsorption. On NaDodSO4/polyacrylamide gels without reduction, it appeared to have a slightly faster migration rate than the C4b-binding protein dissociated from the complex with protein S. After reduction, the subunits of the two forms of C4b-binding protein appeared to have identical molecular weights. Furthermore, there is an equilibrium between free and bound protein S in plasma. The role of protein S in the complex is unknown.
D001464:Barium / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D003169:Complement Inactivator Proteins; D004591:Electrophoresis, Polyacrylamide Gel; D006023:Glycoproteins / Q000378:metabolism*; D006801:Humans; D046911:Macromolecular Substances; D008970:Molecular Weight; D011485:Protein Binding; D017293:Protein S
D002352:Carrier Proteins; D003169:Complement Inactivator Proteins; D006023:Glycoproteins; D046911:Macromolecular Substances; D017293:Protein S; D001464:Barium