Enhancement by heparin of thrombin-induced antithrombin III proteolysis: its relation to the molecular weight and anticoagulant activity of heparin.
Previous findings indicated that binding of heparin to antithrombin III (AT III) facilitates thrombin-induced proteolysis of the inhibitor. We now studied this property of heparin in regard to its molecular weight and anticoagulant activity. Commercial heparin was resolved on Sephadex G-200 into six fractions of decreasing molecular weight. From each fraction high affinity (HA) heparin was isolated by chromatography on AT III-Sepharose and examined in reaction of alpha-thrombin with a molar excess of 125I AT III. Proteolysis of the inhibitor was assessed by SDS polyacrylamide gel electrophoresis. In the presence of the HA heparin from 18% to 38% of AT III participating in reaction appeared in the form of inactive 50,000-dalton fragment, as opposed to 7% of AT III fragmented in the absence of heparin. Although the ability to potentiate proteolysis was at its peak in the medium-molecular-size heparin fraction, the amount of degraded inhibitor relative to anticoagulant activity increased with decreasing molecular weight of the polysaccharide. These findings are consistent with the possibility that the ability of bound heparin to facilitate the cleavage of AT III by thrombin is generally less contingent upon secondary characteristics of the polysaccharide than the anticoagulant activity.
D000990:Antithrombin III / Q000378:metabolism*; D005591:Chemical Fractionation; D002850:Chromatography, Gel; D004357:Drug Synergism; D004591:Electrophoresis, Polyacrylamide Gel; D006493:Heparin / Q000494:pharmacology*; D006801:Humans; D007457:Iodine Radioisotopes; D008970:Molecular Weight; D011485:Protein Binding; D013917:Thrombin / Q000494:pharmacology
D007457:Iodine Radioisotopes; D000990:Antithrombin III; D006493:Heparin; D013917:Thrombin