Proteolysis of bovine and human prothrombin and of bovine factor x by rat mast cell proteinase

The α-chymotrypsin-like proteinase from rat peritoneal mast cells (RMCP I) rapidly destroyed the normal clotting activity of purified, calcium-free, bovine prothrombin, human prothrombin and bovine factor X and simultaneously removed similar N-terminal peptides (M approximately 5000) from both prothrombin and the ‘light’ chain of rfactor X. The amino acid composition of the peptides agreed with the known composition of the regions of the respective parent molecules where γ-carboxyglutamic acid residues are situated. Ca 2+ ions protected each of the proteins from proteolysis and loss of procoagulant activity. Prolonged incubation in the standard physiological assay medium used for prothrombin or treatment with Echis carinatus venom indicated that the thrombogenic portion of prothrombin survived proteolysis by RMCP I. This restricted proteolysis was confirmed by electrophoretic analysis.