The protein composition of the fibrinoid material at the human uteroplacental interface

Uteroplacental fibrinoid was dissected from the maternal face of term human placentae. The ultrastructural appearance of the isolated material was similar to that previously described for fibrinoid in situ by other workers. The material was difficult to dissolve in the absence of SDS and reducing agents and had a carbohydrate content of 4.4–9.4 mg per 100 mg protein. On sodium dodecyl sulphate gel electrophoresis, the major polypeptides in fibrinoid had molecular weights of 55000 and 105000. A variable amount of material at 48000 was also observed, as were many other more minor polypeptide components. The major polypeptides had molecular weights very similar to the γ,β and γ−γ dimer polypeptides of blood fibrin. CNBr mapping showed that the fibrinoid polypeptides of 55000 and 105000 mol.wt had methionine peptides in common with fibrin β and γ−γ chains, respectively. The 55000 mol.wt fibrinoid polypeptide and the β chain of fibrin were both slighly smaller than the β chain of fibrinogen, implying that the polypeptide in fibrinoid was in fact a β chain lacking fibrinopeptide B. There was a variety of other polypeptides in the fibrinoid, of which those over 105000 mol.wt were particularly prominent. They are probably distinguishable from high molecular weight components of fibrin in that they bind 125I-wheatgerm agglutinin most avidly. These results are the first biochemical analysis of uteroplacental fibrinoid. They confirm the presence of fibrin/fibrinogen type protein and show that it is mainly in the form of fibrin. They show that the layer is not particularly rich in carbohydrate and give little support for the view expressed previously that uteroplacental fibrinoid is primarily a product of living or lysed trophoblastic and uterine cells.