Plasminogen activity

Abstract

Plasminogen is present in plasma as a proenzyme with respect to its major catalytic activity, namely the hydrolysis of fibrin and other components in blood. Other activities of plasminogen (e.g. its binding to fibrin, histidine-rich glycoprotein HRGP, and plasmin inhibitor PI), are partly or fully expressed in plasma by the proenzyme form and will not be discussed further here. The measurement of the plasminogen molecule in plasma has presented difficulties for many years, due to its presence in plasma as a proenzyme and the interference of a number of plasmin inhibitors (notably PI) with the measurement of the activated form of the proenzyme, namely plasmin. Plasma plasminogen levels can be measured directly or indirectly. Indirect methods are based on the activation of the inactive plasminogen by streptokinase (SK) or urokinase (UK) to active plasmin which, being a proteolytic enzyme, can be assayed using a variety of methodologies and substrates. The substrates most commonly used have been gelatin¹, fibrinogen-fibrin^2–5, casein^6–10 and esters of arginine and lysine^11–14. Further details of methods and substrates for the assay of plasmin have been reviewed¹⁵. Most direct assay methods for plasminogen are based on its affinity for a plasminogen antiserum, and have also been reported in the literature^16–20. A listing of some of the assays with references is given in Table 27.1