Plasmin

E.C. 3.4.21.7
Synonyms: fibrinase; fibrinolysin; actase; serum tryptase; thrombolysin

On this page:

• Products
• Physical Properties
• Specificity and Kinetics
• Inhibitors
• Substrates
• Solubility and Solution Stability

Physical Properties and In vivo processing
Plasminogen:
Plasminogen is the precursor to the fibronolytic protease plasmin as well as angiostatin, an angiogenesis/tumor metastasis inhibitor. Human prostate carcinoma cells release urokinase and free sulfhydryl donors which can produce angiostatin from plasminogen. In vitro, urokinase, tissue plasminogen activator, or streptokinase, in combination with sulfydryl donors, such as N-acetyl-L-cysteine, D-penicillamine, captopril, L-cysteine, or reduced glutathione, produced angiostatin from plasminogen.¹
Native-intact human plasminogen is a 291 amino acid glyco-protein with as many as 24 disulfide bonds. Plasminogen contains a single N-linked sialylated biantennary glycan. The two O-glycans possess a Gal β-1-3GalNAc core which is α-2-3 sialylated at the terminal Gal. An additional disialylated form has a second sialic acid residue with an α-2-6 linkage to GalNAc. Mono- and disialylated forms occur at a molar ratio of 80:20 in human plasminogen.^2,3

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Plasmin:
MW: ~86 kDa⁴ (Human)
When run on SDS-PAGE, bands appeared at 68, 46.2, 23.1 and 12.3 kDa.

Plasmin is a serine endopeptidase of the peptidase S1 family. Plasmin is converted to plasminogen by cleavage between Arg561 and Val562. The resulting activated plasmin consists of two disulfide-linked polypeptide chains. The plasmin heavy chain (MW 60 kDa) is derived from the amino terminal region of plasminogen. The light chain originates from the carboxyl-terminus of plasminogen. In vivo, the MW of the heavy chain can vary from 63KDa to 12KDa depending on the extent of proteolysis to the plasminogen from which it is derived. Plasmin is activated by a variety of proteases including urokinase, tissue plasminogen activator, and streptokinase. During the activation of plasminogen, an autolytic peptide of molecular weight 8,200 is released from the Glu-amino terminus to yield a Lys-amino terminus on the heavy chain. The active site of plasmin is on the light chain.¹

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Specificity and Kinetics
Plasmin exhibits preferential cleavage at the carboxyl side of Lysine and Arginine residues with higher selectivity than trypsin.⁵ It converts polymerized fibrin into soluble products.

pH Optimum: 8.5
pH 7.5: about 40% of maximal activity, pH 9.5: about 50% of maximal activity⁶

Temperature Optimum: 37 °C with rapid inactivation at 56 °C⁶

Solubility and Solution Stability
Plasmin is readily soluble in water (1 mg/ml). Solutions should be kept on ice and discarded at the end of the day or aliquoted and frozen at a concentration of 1 mg/ml. Frozen solutions will lose approximately 10% activity per month.

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References

1. Gatley, S., et al., Proc. Natl. Acad. Sci. U S A, 94, 10868–10872 (1997)
2. Marti, T., et al., Eur J Biochem., 173, 57-63 (1988)
3. Pirie-Shepherd, S.R., et al., J Biol. Chem.,272, 7408-11 (1997)
4. Trends Biochem. Sci., 4, 1 (1979)
5. IUBMB Enzyme Nomenclature: www.chem.qmul.ac.uk/iubmb/enzyme/EC3/4/21/7.html
6. Greig, B.H.W., et al., Biochim. Biophys. Acta, 67, 658-668 (1963)

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