Will elevated levels of plasminogen interfere with the Chromogenix Coamatic® Plasmin Inhibitor test?
No, elevated plasminogen levels should not effect the results. Residual plasmin hydrolyzes the chromogenic substrate, but the principle of plasminogen is different. No part is played by plasmin. Instead, determination by chromogenic substrate requires all plasminogen in the sample to be activated to plasminogen/streptokinase complex, which hydrolyzes the chromogenic substrate.
|Protein S||70||10 (free)||0.14|
|Heparin Cofactor II||66||80||1.2|
|Protein C Inhibitor||57||4||0.07|
The plasminogen present in the sample is activated by the addition of an excess of streptokinase (Sk) forming a plasminogen-streptokinase (Plg/Sk) complex. Plg-depleted fibrinogen is included in the Sk reagent in order to avoid the risk of overestimation of Plg in the pathological plasmas containing elevated levels of fibrinogen (Fib) and/or fibrin degradation products (FDP). The PlgSk/Fib complex is determined by the rate of hydrolysis of the chromogenic substrate S-2403™. The pNA release measured at 405 nm is proportional to the plasminogen activity level of the plasma sample.
Plasminogen is activated by endogenous, natural activators, and exogenous activators. Activation by its natural activators, tPA and uPA, involves a bond cleavage at a specific site in the plg molecule, which gives rise to a two-chain molecule linked by two disulfide bonds. tPA binding to fibrin concentrates and correctly orientates the tPA and plasminogen, as well as inducing a conformational changes in the molecules that promote efficient clot lysis. uPA can only activate plasminogen in the presence of fibrin, but it does not bind to, nor is it activated by fibrin. Streptokinase is an exogenous plasminogen activator and functions by forming a 1:1 complex with human plg. This complex can function as an activator of other plg molecules. Complex formation is accompanied by a conformational change in the plg molecule, exposing the active site.
Describe the types of plasminogen deficiency. What are the clinical conditions associated with decreased plasminogen levels? With elevated plasminogen levels?
Plasminogen deficiency can be hereditary or acquired. There are two types of hereditary plg deficiency. Hypoplasminogenemia, also called type I, is characterized by a parallel reduction of both plasminogen antigen and activity to about 50% of normal. Dysplasminogenemia, or type II, is characterized by a reduced activity/antigen ratio, meaning that the activity level is more reduced than the antigen level. Hereditary plg deficiency is usually associated with either a thrombotic or a hyperfibrinolytic condition. It has been estimated that type I and II deficiency accounts for 2-3% of unexplained DVT in young patients, and is associated with an increased risk for thrombosis, although just how much of a risk increase is still controversial. Elevated plasminogen levels are sometimes associated with situations such as pregnancy, oral contraceptives, obesity, or hypothyroidism.
Plasminogen is the inactive precursor of plasmin, a potent serine protease involved in the dissolution of fibrin clots in blood. Human plasminogen is a single-chain glycoprotein with a molecular mass of 92 kDa. The N-terminal portion of the plasminogen molecule consists of five kringle domains with the capacity to bind to fibrin. The kringles control the ability of plg to adopt different conformations. The protease domain resembles that of the other serine proteases and contains the active site His, Asp, Ser. The region also contains Ala, which appears to be essential for the normal function of plasminogen, since mutation from Ala601 to Thr601 (alanine to threonine point mutation) leads to an increased risk of thrombosis.
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. For example, a plasminogen reagent when activated to plasmin with streptokinase can show an 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.
What is the difference between Glu-plasminogen and Lys-plasminogen? How can the two forms be measured?
The native form of plasminogen in plasma has glutamic acid (Glu) at the N-terminal and is termed Glu-plasminogen. Other plasminogen forms generated by the catalytic cleavage of plasmin and containing mostly lysine (Lys) at the N-terminal position are termed Lys-Plasminogen. They can be measured using a chromogenic method based on the different rate of activation of the two forms by urokinase. See Scully MF, Kakkar VV. Measurement of Degraded Forms of Plasminogen in Human Plasma. Thromb Res (1980); 17: 347-352. Note that the Chromogenix plasminogen is at least 95% Glu-plasminogen.
We sell both forms, though most researchers want Glu-Plasminogen, which is a preparation of at least 95% Glu-plasminogen. See the product pages for detailed information about our plasminogen preparations.