Plasmin Activity

1 mg of plasmin contains 24 CU or 28 CTA-U.

Our purified plasmins (HPLM, BPLM, MPLM, RPLM, RbPLM) are 100% active because they are purified on immobilized SBTI, which only binds functionally active plasmin.

The amount of plasminogen in 1 ml of normal plasma (approximately 0.2 mg) corresponds to 3.8 CU or 27.74 nkat S-2251 when activated by streptokinase (1). In 1983 Friberger (2) reported that 1 µg of human plasmin corresponds to 0.20 nkat S-2251, or to 0.024 CU or to 0.028 CTA-U. This specific activity conversion factor can also be applied to plasmin from other species. In 1975 a preparation of partially purified plasmin in 50% glycerol was established as an international reference preparation (3). The World Health Organization defined the International Unit of Plasmin as the activity contained in 0.125 ml of the International Reference Preparation of Plasmin (4).

nkat S-2251 – 1 nkat = 1 x 10-9 mol of product released per second from plasmin substrate S-2251
CU – Casein Units
CTA-U – Committee on Thrombolytic Agents (CTA) Units

1. Friberger P and Knos M. Plasminogen activation in normal plasma. In: Chromogenic peptide substrates, Eds, Scully MF and Kakkar VV, Churchill Livingstone, 128-140 (1979).
2. Friberger P et al. Synthetic peptide substrate assays and fibrinolysis and their application on automates. In: Seminars in Thrombosis and Haemostasis, Vol. 9, 281-300 (1983).
3. Kirkwood TB et al. A standard for human plasmin. Thromb Diath Haemorrh 34, 20-30 (1975).
4. 28th Report, WHO Expert Committee on Biological Standardization. WHO Tech Rep Ser No 610; 1977, pp 13.

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