A difference between plasma and cellular fibronectins located with monoclonal antibodies.

We describe the properties of two monoclonal antibodies to hamster cellular fibronectin. One of them exhibits a marked specificity for cellular fibronectin, whereas the other recognized both cellular and plasma fibronectins. However, both antibodies recognize determinants in the same restricted region of cellular fibronectin, located near to but not at the C-terminal and of the intact molecule. Tryptic and chymotryptic digestions release this portion of the molecule in 40 kd fragments that contain a free sulfhydryl group. Recognition of fibronectin by these two monoclonal antibodies does not require the presence of carbohydrate residues on the fibronectin. These monoclonal antibodies allow location of a structural difference between the two forms of fibronectin and should permit further analysis of this difference.