The Oligosaccharide of Human Thrombin: Investigations of Functional Significance

Functional properties of the carbohydrate chain of human thrombin were examined by quantitating the activity of the enzyme before and after partial removal of its oligosaccharide by exoglycosidases. The following activities were studied: fibrinogen clotting, factor VIII coagulant (VllI:C) activation, inhibition by defibrinated plasma (anti-throm-bin-lll and α2-macroglobulin), binding to polymerized fibrin, and stimulation of platelet release and aggregation. In general, the published information about the activity of native thrombin in these interactions was confirmed, though differences were observed in the association constants describing thrombin binding to fibrin. Partial degly-cosylation had no apparent effect on any of these activities. It is concluded, therefore, that the oligosaccharide of human thrombin is located outside the major protein and platelet-binding regions of the molecule.