The activity of plasmin and plasminogen is expressed in CU. What is this, and what is the equivalent in nkat?

CU stands for Casein Units, and is a measure of the proteolytic activity on the substrate casein. The plasminogen reagent when activated to plasmin with streptokinase shows and activity of 7.3 nkat_S-2251 per CU. 1 mg of plasmin corresponds to 0.20 nkat_S-2251, or to 0.024 CU.