[Fibronectin-synthesizing activity of free and membrane-bound polyribosomes from human fibroblasts and chick embryos].

Using immunochemical methods, the fibronectin-synthesizing activity of membrane-bound and free polyribosomes in a cell-free system was studied. It was demonstrated that fibronectin biosynthesis on membrane-bound polyribosomes from human embryonic fibroblasts makes up to 4.9%, while that from chicken embryos--1.1% of the total amount of the de novo synthesized proteins (as compared to 1.0 and 0.3% in free polyribosomes, respectively). Fibronectin monomers (Mr = 330 kD) were detected only in the newly synthesized (in the presence of spermidine) material of the cell-free system containing heavy fractions of membrane-bound polyribosomes.