Target size for a fibronectin-cell adhesion system determined by the X-ray inactivation method.

In order to elucidate the mechanism of cell adhesion, the size of the functional site, both in the fibronectin molecule and in the mouse fibroblast cell, responsible for cell adhesion activity, was determined. The size was assumed to be equivalent to the target size, that can be determined from the X-ray inactivation dose. The target size of the cell-binding site in the fibronectin molecule was 32 kdalton. The molecular weight was much larger than that of the tripeptide, which has been reported to be the minimum peptides having a cell-binding activity. This suggests that submolecular regions in fibronectin other than the tripeptide are necessary for cell adhesion. The target size in the cell responsible for the adhesion to the fibronectin-coated surface was 4300 kdalton. The large molecular weight of the target could be explained by assuming that a complex protein system is involved in the cell-adhesion process in the cell.