We have tested the ability of various glycosaminoglycans to increase the rate of inhibition of thrombin by heparin cofactor II (HCII) and by antithrombin III (ATIII) isolated from human plasma. Heparin, dermatan sulfate, and heparan sulfate from bovine liver (in order of decreasing activity) activated HCII. In contrast, only heparin and bovine liver heparan sulfate activated ATIII, whereas dermatan sulfate was inactive at concentrations less than or equal to 1 mg/ml. Heparan sulfate from human

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... orta, chondroitin 4-sulfate, chondroitin 6-sulfate, keratan sulfate, and hyaluronic acid had little or no activity with either HCII or ATIII. The second order rate constant for the thrombin-HCII reaction reached a maximum value of 6.4 X 10(8) M-1 min-1 in the presence of 250-500 micrograms/ml of dermatan sulfate compared to 3.8 X 10(8) M-1 min-1 in the presence of 40-80 micrograms/ml of heparin. When 125I-thrombin was incubated with plasma in the presence of greater than or equal to 100 micrograms/ml of dermatan sulfate, the protease became complexed exclusively with HCII, suggesting that HCII is the only thrombin inhibitor in human plasma that can be activated by dermatan sulfate.