FREEZE-DRIED FIBRINOGEN OR FIBRINOGEN IN EDTA STIMULATE THE TISSUE-TYPE PLASMINOGEN ACTIVATOR-CATALYZED CONVERSION OF PLASMINOGEN TO PLASMIN

Both soluble and insoluble fibrin stimulate the tissue-type plasminoge n activator-catalysed conversion of plasminogen to plasmin. Whether fi brinogen can exert a similar effect has been a controversial issue. Th e present investigation shows that while fibrinogen purified by beta-a lanine precipitation does not stimulate the tissue-type plasminogen ac tivator-catalysed plasminogen activation, fibrinogen which has been ei ther lyophilized or stripped of bound Ca2+ ions by EDTA chelation, sti mulates this reaction. The data indicate that such procedures alter th e molecular conformation of fibrinogen, and expose stimulatory sites w hich are hidden in the native fibrinogen molecule. These results may e xplain previous findings concerning the capacity of fibrinogen as a st imulator of the tissue-type plasminogen activator-catalysed plasminoge n activation. Since even slight alteration of the molecular structure of fibrinogen leads to an increase in the tissue-type plasminogen acti vator stimulation, the authors suggest that this can be used to test i f the fibrinogen is in a native state.