Comparative studies of heparin cofactor activity toward antithrombin III and heparin cofactor II, and antithrombin III affinity between low molecular weight heparin and unfractionated heparin.

The accelerating effects of an UF heparin (Novo) and two LMW heparins (Fragmin and PK 10169) on AT III and HC II were investigated in a purified system. The effects of these heparins on APTTs were examined using human plasma. Fractionation of these heparins by affinity column chromatography yielded the following results: UF heparin was separated into two distinct fractions, LA and HA for AT III. Both LMW heparins were separated into three fractions: NA, LA, and HA for AT III. The accelerating effects of these fractions on both antithrombin and anti-Factor Xa activity of AT III were dependent on the strength of their affinity to AT III. The accelerating effects of these fractions on the antithrombin activity of HC II was independent of the strength of their affinity for AT III. LA had a much stronger anticoagulant activity of HC II toward thrombin than did HA. It is concluded that LA for AT III is necessary to show HC II activity.