Inaccessibility to ligands of the amino-terminal region of plasma fibronectin.

Fragments of plasma fibronectin can display properties not expressed by fibronectin. This work shows that the relative affinities of smaller fragments for gelatin or heparin increases with decreasing fragment size. When heparin or gelatin were added to fragments or to fibronectin, the affinities for the alternate ligand increased. The UV and CD spectra of a mixture of amino-terminal 29-kD and 50-kD fragments differed from that of the precursor, the intact 72-kD fragment, suggesting differences in secondary structure. Therefore, biologic activities of the 29-kD and 50-kD segments in fibronectin may be suppressed by structural constraints but may be expressed more fully by interaction with ligands.