Summary
Two high affinity heparin fragments (A/r 4,300 and M, 3,200) were covalently coupled to antithrombin III (J. Biol. Chem. 1982; 257: 3401-3408)
with an apparent 1:1 stoichiometry and a 30-35% yield.
The purified covalent complexes inhibited factor Xa with second order rate constants
very similar to those obtained for antithrombin III saturated with these heparin fragments
and to that obtained for the covalent complex between antithrombin III and native
high affinity heparin.
The disappearance rates from plasma in rabbits of both low molecular weight heparin
fragments and their complexes could adequately be represented by two-compartment mammillary
models. The plasma half-life (t'/j) of both low Afr-heparin fragments was approximately 2.4 hr. Covalent coupling of the fragments to
antithrombin III increased this half-life about 3.5 fold (t1/2 ≃ 7.7 hr), approaching
that of free antithrombin III (t1/2 ≃ 11 ± 0.4 hr) and resulting in a 30fold longer
life time of factor Xa inhibitory activity in plasma as compared to that of free intact
heparin (t1/2 ≃ 0.25 ± 0.04 hr).
Keywords
Covalent low molecular weight heparin-antithrombin III complexes - Anti-factor Xa
activity - In vivo plasma half-life (t1/2) - Anticoagulant activity