线性范围:156 - 10,000 pg/ml.Fibronectin is a high-molecular weight (~440kDa) glycoprotein of the extracellular matrix that binds to membrane-spanning receptor proteins calledintegrins.Similar to integrins, fibronectin binds extracellular matrix components such as collagen, fibrin, and heparan sulfate proteoglycans (e.g.syndecans).
Fibronectin exists as a protein dimer, consisting of two nearly identical monomers linked by a pair of disulfide bonds.The fibronectin protein is produced from a single gene, but alternative splicing of its pre-mRNA leads to the creation of several isoforms.
Plasma fibronectin, which is synthesized by hepatocytes,and fibronectin synthesized by cultured fibroblasts are similar but not identical; immunological, structural, and functional differences have been reported.It is likely that these differences result from differential processing of a single nascent mRNA. Nevertheless, plasma fibronectin can be insolubilized into the tissue extracellular matrix in vitro and in vivo. Both plasma and cellular fibronectins in the matrix form high molecular weight, disulfide-bonded multimers. The mechanism of formation of these multimers is not presently known. Plasma fibronectin has been shown to contain two free sulfhydryls per subunit (X), and cellular fibronectin has been shown to contain at least one. These sulfhydryls probably are buried within thetertiary structure, because sulfhydryls are exposed when the fibronectin is denatured. Such denaturation results in the oxidation of free sulfhydryls and formation of disulfide-bonded fibronectin multimers. This has led to speculation that the free sulfhydryls may be involved in formation of disulfide-bonded fibronectin multimers in the extracellular matrix. Consistent with this, sulfhydryl modification of fibronectin with N-ethylmaleimide prevents binding to cell layers. Tryptic cleavage patterns of multimeric fibronectin do not reveal the disulfide-bonded fragments that would be expected if multimerization involved one or both of the free sulfhydryls. The free sulfhydryls of fibronectin are not required for the binding of fibronectin to the cell layer or for its subsequent incorporation into the extracellular matrix. Disulfide-bonded multimerization of fibronectin in the cell layer occurs by disulfide bond exchange in the disulfide-rich amino-terminal one-third of the molecule.