[Comparative study of the proteolytic products of fibronectins in the serum of adult and embryonic animals formed under the effects of proteinases of the spleen].

The effects of two spleen proteinases, cathepsin D and thiol proteinase I active in neutral media--on the structural properties of fibronectins from blood plasma on adult animals and their embryos were investigated. Proteinase I and cathepsin D caused rapid fragmentation of all fibronectins under study. Fibronectin from calf embryonic serum was more sensitive to proteinase I than that from adult animal serum. The molecular weight and the correlation between the proteolytic products formed under the influence of each enzyme, on the embryonic and "adult" fibronectins, are very similar but not identical. Similar results were obtained in experiments with proteolytic products of chicken serum and embryo fibronectins. Fragmentation of embryonic fibronectin occurs more rapidly than that of chicken fibronectin; the fibronectin proteolytic products differ both qualitatively and quantitatively. However, the determination of structural differences between these fibronectins is considerably hampered by the presence of protein contaminations in chicken fibronectin preparations.