Functional analysis of plasma fibronectin with special consideration of binding interferences

So far, soluble fibronectin has been quantitated mostly by immunological techniques. In this investigation we show that an immunological assay provides reliable results only with intact fibronectin. Fibronectin fragments resulting from proteolysis give rise to falsely raised values. We present four functional tests based on the sandwich (ELISA) technique on microtitre plates. These quantify fibronectin on the basis of its binding capacity to collagen, heparin, fibrin and carboxy-group-modified IgG with high sensitivity, specificity and precision. Analysis of the bioactivity spectrum of intact fibronectin is not disturbed by fibronectin fragments. Furthermore we demonstrate interferences, in particular between heparin and collagen in their mutual binding to fibronectin. This provides new indications of a "substrate activation" of fibronectin.