Binding of PPACK-thrombin. Binding of native α-thrombin was compared with that of proteolytically inactivated thrombin (PPACK-thrombin) in L2H/V cells. Data for binding of α-thrombin to L and L2H cells and of PPACK-thrombin to L2H cells are shown for comparison. Binding was evaluated as in Fig 1. Binding of native thrombin or PPACK-thrombin to L2H/V cells was significantly greater than to the other cell lines (Student's t test: n = 6, t = 11.240, P < .001). The difference in binding to L2H/V cells between native thrombin and PPACK-thrombin did not reach statistical significance (P = .223).