Binding of fibronectin to actin is inhibited by gelatin

An enzyme-linked immunosorbent assay was developed to study the ability of fibronectin to bind to actin. Plastic microtiter wells were coated with actin and the binding of fibronectin was detected using purified fibronectin antibodies conjugated to alkaline phosphatase. The binding was dependent on the concentration of actin used for coating and on the amount of fibronectin that was subsequently permitted to bind. The binding could be inhibited by actin and gelatin, but not by heparin or bovine serum albumin. No major inhibition was observed by amines known to interfere with some of the other interactions of fibronectin. The ability of gelatin to inhibit the binding suggests that actin and collagen cannot bind to fibronectin simultaneously, and that the cell-binding and actin-binding sites of fibronectin are separate since cells attach to collagen-bound fibronectin.