U. Haddeland et al., AGGREGATED, CONFORMATIONALLY CHANGED FIBRINOGEN EXPOSES THE STIMULATING SITES FOR T-PA-CATALYZED PLASMINOGEN ACTIVATION, Thrombosis and haemostasis, 75(2), 1996, pp. 326-331
The present paper shows that conformationally changed fibrinogen can e
xpose the sites A alpha-(148-160) and gamma-(312-324) involved in stim
ulation of the tissue-type plasminogen activator (t-PA)-catalysed plas
minogen activation. The exposure of the stimulating sites was determin
ed by ELISA using mABs directed to these sites, and was shown to coinc
ide with stimulation of t-PA-catalysed plasminogen activation as asses
sed in an assay using a chromogenic substrate for plasmin. Gel permeat
ion chromatography of fibrinogen conformationally, changed by heat (46
.5 degrees C for 25 min) demonstrated the presence of both aggregated
and monomeric fibrinogen. The aggregated fibrinogen, but not the monom
eric fibrinogen, had exposed the epitopes A alpha(148-160) and gamma-(
312-324) involved in t-PA-stimulation. Fibrinogen subjected to heat in
the presence of 3 mM of the tetrapeptide GPRP neither aggregates nor
exposes the rate-enhancing sites. Thus, aggregation and exposure of t-
PA-stimulating sites in fibrinogen seem to be related phenomena, and i
t is tempting to believe that the exposure of stimulating sites is a c
onsequence of the conformational changes that occur during aggregation
, or self-association. Fibrin monomers kept in a monomeric state by a
final GPRP concentration of 3 mM do not expose the epitopes A alpha-(1
48-160) and gamma-(312-324) involved in t-PA-stimulation, whereas dilu
tion of GPRP to a concentration that is no longer anti-polymerizing, r
esults in exposure of these sites. Consequently, the exposure of t-PA-
stimulating sites in fibrin as well is due to the conformational chang
es that occur during self-association.