Cell-substratum interactions: serum spreading factor.

We have prepared a fraction of commercial fetal calf serum whose major component comprises proteins of apparent molecular mass 65-80 kDa. These preparations elicit cell spreading responses in serum-free medium at concentrations similar to those reported for human vitronectin. In addition, we have identified (by a protein blotting technique) the 65-80 kDa component as the active species in our preparations. Cell spreading responses in the presence of our 'bovine vitronectin' preparations are similar to cell spreading on fetal calf serum. (In contrast, cell spreading on bovine fibronectin showed very different kinetics). Our results suggest that bovine vitronectin may be an important component of fetal calf serum involved in conditioning cell culture substrata.