Summary
Human fibrinogen was subjected to limited proteolytic attack by thrombin, batroxobin
or Agkistrodon contortrix thrombin-like enzyme, yielding desAB-, desA- or desB-fibrin
monomers, respectively. Turbidity curves demonstrated that, with all three enzymes,
the polymerization process was strongly accelerated by increasing the calcium concentration
from 10−5 M to 10−4 M. Synthetic peptide Gly-His-Arg (5 mM), an analogue of the aminoterminal sequence
of fibrin β-chain, inhibited aggregation of desB-fibrin monomers at physiological
calcium concentration whereas it enhanced aggregation of desA- and desAB-fibrin monomers
at calcium concentrations below 10−4 M. On the other hand, Gly-Pro-Arg (1 mM) corresponding to the amino-terminus of fibrin
α-chain, dramatically inhibited aggregation of both desA- and desB-fibrins, but it
only moderately affected the polymerization of thrombin-induced monomers. We conclude
that the observed effects of Gly-Pro-Arg and Gly-His-Arg are not due solely to their
competition with fibrin amino-termini for the respective binding sites in the D-domain,
but rather reflect conformational changes in fibrin monomers which affect the polymerization
process.
Key words
Fibrin aggregation - Fibrinopeptides - Synthetic peptides - Calcium
