Human Fibrinogen Binds Edta And Citrate

It was shown that EDTA and citrate make the carboxy-terminal parts of the γ-chains of fibrinogen more susceptible to plasmin degradation. This is an effect independent of the calcium-chelating properties of those compounds. Furthermore, EDTA prolongs the thrombin times decreases the heat stability and causes the formation of abnormal clots.This suggests a direct interaction of EDTA (and possibly also of citrate) with the fibrinogen molecule thereby causing a conformational change. The interaction of citrate and EDTA with fibrinogen was measured by direct binding studies (equilibrium dialysis).It was found that at pH 7.5 human fibrinogen binds 3.4 molecules of citrate with Kd = 1.4 x 10-4M or 0.4 molecules of EDTA with Kd = 2.2 x 10-5M. Citrate and EDTA compete for the same binding site(s). No binding of acetate could be demonstrated.The binding of EDTA and citrate shows a strong ^-dependence suggesting a (partly) ionogenic binding between charged areas on the fibrinogen molecule and charged groups on EDTA or citrateOur results support the idea that the binding of EDTA and citrate and the concomitant effect on the plasmin attack are independent of the effect of calcium ions