Plasmin

• OMIM: 173350
• UniProt: P00747

• CAS Number: 9001-90-5

Plasmin is an enzyme from the group of peptidases which cleave many proteins in blood plasma and can degrade. This property is particularly effective on fibrin in blood clots. The that process, called fibrinolysis ( Fibrinspaltung ).

Plasmin is a serine protease, which is formed from the precursor plasminogen.

Plasminogen

Plasmin is synthesized in a precursor plasminogen by the liver and secreted into the bloodstream and, as such, also be measured. Plasminogen has a biological half-life of 2.2 days. Free, active plasmin is not detectable in normal blood or just in the smallest amount.

Plasminogen is determined from citrated blood. The normal value in the blood is:

• Plasminogen activity 85-110 %
• Plasminogen concentration 0.2 g / l

Human plasminogen was also the first marker that can distinguish by its specific binding reliably between pathologically folded prion protein ( PrPSc ) and the normal cellular form of the protein ( PrPC ).

Function

The main function of plasmin is the Fibrinspaltung. One can refer to the plasmin fibrin - scissors in the coagulation system. Thrombin would be the opposite, that the loom of fibrin clotting.

Also, the soluble precursor of fibrin, fibrinogen, is divided by plasmin in fibrinogen. The fibrin ( ogen) degradation products inhibit the fibrin turn.

The specificity of plasmin to fibrin results from the fact that plasminogen attached to fibrin during clotting and is only activated there.

Serine proteases such as plasmin develop irreversible effects. This is in contrast to most other enzymes that catalyze biochemical reactions in both directions.

As a serine protease, plasmin has also in its amino acid sequence, the so-called catalytic triad

• Serine 195,
• Histidine 57 and
• Aspartic acid 102

Plasmin acts autocatalytically that is, converts it to other molecules of plasminogen to active plasmin: The proenzyme is therefore substrate of the activated enzyme.

T-PA ( plasminogen activator )            u -PA              ↓ Plasminogen plasmin →                   ↓            Fibrin, fibrin degradation products → In addition to its fibrinolytic activity of plasmin can cleave various other proteins:

• It activates collagenases,
• It activates some mediators of the complement
• It dilutes the wall of the Graafian follicle at the beginning of ovulation
• It dissolves fibrin, fibronectin, thrombospondin, laminin and von Willebrand factor (vWF ).

Plasmin also is a very potent activator of monocytes.

In the recovery of the female breast after weaning the Plasminogen-/Plasmin-System plays an important role.

Generally gets plasmin and plasminogen in certain amounts from the blood into the milk, which is also in cow's, sheep's and goat's milk, especially for the production of cheese has a meaning, as caused by the proteolytic activity of plasmin specific cleavage products with a specific flavor.

The efficacy of oral plasmin as tumor-inhibiting substance is unproven and unlikely, since plasmin is destroyed by the digestive system.

Activation

Plasminogen is activated by the following substances:

• Tissue plasminogen activator ( = tissue plasminogen activator ) tPA,
• Urokinase plasminogen activator (uPA )
• Streptokinase
• Fibrin ( factor Ia)

Inactivation

It is inactivated by the following substances:

• Of course Alpha 2 - antiplasmin, a serine protease inhibitor
• Alpha-2 -macroglobulin

• Aprotinin
• ε -aminocaproic acid
• Para- aminomethyl benzoic acid ( PAMBA )
• Tranexamic acid

Aminocaproic acid, para- aminomethyl benzoic acid and tranexamic acid are among the ε -amino carboxylic acids. These are synthetic substances that are similar to lysine. They block the lysine binding site on plasmin, which is essential for enzyme action of plasmin.

Lack of plasmin may lead to thrombosis, since then the clot resolution is not working properly. Arsenic blocks the production of plasmin and unfolds over a portion of its chronic toxicity to the vessels.