The function of calcium in protein C activation by thrombin and the thrombin-thrombomodulin complex can be distinguished by mutational analysis of protein C derivatives.

The abbreviations used are: Gla, 4-carboxyglutamic acid; EGF, epidermal growth factor; GDPC, Gla-domainless protein C, protein C from which residues 1-45 were removed by the recombinant DNA methods; EQPD, protein C lacking residues 1-91, i.e. the Gla domain and the first epidermal growth factor-like repeat; DG167, DG172, or DG167/172, protein C derivatives in which the Asp residues are replaced with a Gly at indicated numbers; PAGE, polyacrylamide gel electrophoresis; PCR, polymerase chain reaction; RSV, ROUS sarcoma virus; Mes, 4-morpholineethanesulfonic acid.