Methods for converting prethrombin-1 to thrombin are disclosed. An aqueous solution of prethrombin-1 is applied to oscutarin-C immobilized on a solid support so as to provide from 500 mg to 4000 mg of prethrombin-1 per mL of the solid support and a contact time between the prethrombin-1 and the oscutarin-C of from 1.8 to 3.5 minutes. The resulting active thrombin may be captured on an ion exchange chromatography medium or an affinity chromatography medium.