Thrombin amidolytic activity assays. The amidolytic activity of thrombin in the presence of equal amounts of conditioned media from mock-transfected Cos cells (CON) or those transfected with pSG5-HV3 (HV3) was determined as described in Materials and Methods using chromogenic substrate S2238 (n = 3, ±mean), with a thrombin concentration of 0.1 nmol/L. D-CON and D-HV3 are the same as CON and HV3, except that the conditioned media were dialyzed before use overnight at 4° using dialysis tubing with MWCO of 12 to 14 kD.