Interaction of factor Xa with heparin does not contribute to the inhibition of factor Xa by antithrombin III-heparin.
Factor Xa modified by reductive methylation (greater than 92%) loses the capacity to bind heparin as determined both by gel chromatography and by sedimentation equilibrium ultracentrifugation. The kinetic properties of methylated factor Xa differ, with respect to KM and Vmax for a synthetic tripeptide substrate and for antithrombin III inhibition rate constants, from those of the unmodified enzyme. The 10,000-fold rate enhancement elicited by the addition of heparin to the antithrombin III inhibition reaction, however, is the same. The observed second-order rate constants (k"obs) for antithrombin III inhibition of factor Xa and methylated factor Xa are 3000 and 340 M-1 s-1, respectively, whereas k"obs values for the inhibition of factor Xa or methylated factor Xa with antithrombin III-heparin are 4 X 10(7) and 3 X 10(6) M-1 s-1, respectively. These findings provide direct evidence that the interaction of factor Xa with heparin is not involved in the heparin-enhanced inhibition of this enzyme.
Owen
B A
BA
Section of Hematology Research, Mayo Clinic and Foundation, Rochester, Minnesota 55905.
Owen
W G
WG
D000818:Animals; D000990:Antithrombin III / Q000494:pharmacology*; D002417:Cattle; D015951:Factor Xa / Q000737:chemistry / Q000378:metabolism*; D065427:Factor Xa Inhibitors; D006493:Heparin / Q000378:metabolism* / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008745:Methylation; D011485:Protein Binding
D065427:Factor Xa Inhibitors; D000990:Antithrombin III; D006493:Heparin; D015951:Factor Xa