Differences in polyamine availability and insertion into fibronectins released from normal and transformed cells.

1. Fibronectin released from transformed rat kidney cells compared with that released from normal rat kidney cells shows a 50% increase in amino group availability. 2. No such changes were observed in thiol and carboxy group availability or in sialic acid content. 3. The increased amino group availability is not due to a greater polyamine content, which was about 0.04 pmol/mg of protein. 4. Transglutaminase mediated the insertion of spermidine into normal cell fibronectin with linear kinetics. With fibronectin from transformed cells (temperature-sensitive mutant or wild-type), kinetics typical of substrate inhibition were observed. 5. Immunochemical analysis with an anti-polyamine antiserum and an anti-(human fibronectin) antiserum showed that fibronectins from normal and transformed cells react differently. The significance of these results is discussed in the light of changes in the secondary structure between the two fibronectins.