FIBRIN STRUCTURES DURING TISSUE-TYPE PLASMINOGEN ACTIVATOR-MEDIATED FIBRINOLYSIS STUDIED BY LASER-LIGHT SCATTERING - RELATION TO FIBRIN ENHANCEMENT OF PLASMINOGEN ACTIVATION
R. Bauer et al., FIBRIN STRUCTURES DURING TISSUE-TYPE PLASMINOGEN ACTIVATOR-MEDIATED FIBRINOLYSIS STUDIED BY LASER-LIGHT SCATTERING - RELATION TO FIBRIN ENHANCEMENT OF PLASMINOGEN ACTIVATION, European biophysics journal, 23(4), 1994, pp. 239-252
The aim was to relate fibrin structure and the stimulatory effect of f
ibrin on plasminogen activation during t-PA-mediated fibrinolysis usin
g Lys(78)-plasminogen as activator substrate. Structural studies were
undertaken by static and dynamic laser light scattering, cryo transmis
sion electron microscopy and by the measurement of conversion of fibri
n to X-, Y- and D-fragments. The kinetics of plasmin formation were mo
nitored by measurement of the rate of pNA-release from Val-Leu-Lys-pNA
. The process of fibrin formation and degradation comprised three phas
es. In the first phase, protofibrils with an average length of about 1
0 times that of fibrinogen were formed. The duration of this phase dec
reased with increasing t-PA concentration. The second phase was charac
terized by a sudden elongation and lateral aggregation of fibrin fiber
s, most pronounced at low levels of t-PA, and by formation of fragment
X-polymer. The third phase was dominated by fragmentation of fibers a
nd by formation of Y- and D-fragments. Plasmin degraded the fibers fro
m within, resulting in the formation of long loose bundles, which subs
equently disintegrated into thin filaments with a length of less than
10 and a mass per length close to one relative to fibrinogen. Plasmin
generation at high t-PA concentrations sets in just prior to (and at l
ow t-PA concentrations shortly after) the onset of the rapid second ph
ase of elongation and lateral aggregation of fibrin fibers. The maxima
l rate of plasmin formation per mol t-PA was the same at all concentra
tions of activator and was achieved close to the time of the peak leve
l of fragment X-polymer. Plasmin formation ceased after formation of s
ubstantial amounts of Y- and D-fragments. At this stage the length was
between 300 and 3 and the mass per length close to 1, both relative t
o fibrinogen. In conclusion our results indicate that (1) formation of
short fibrin protofibrils is the minimal requirement for the onset of
the stimulatory effect of fibrin on plasminogen activation by t-PA, (
2) formation of fragment X protofibrils is sufficient to induce optima
l stimulation of plasminogen activation, and (3) plasmin degrades late
rally aggregated fibrin fibers from within, resulting in the conversio
n of the fibers into long loose bundles, which later disintegrate into
thin filaments.