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Protein C

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Haematologic Technologies, Inc.

57 River Road

Essex Junction, VT USA

Tel: 802.878.1777

Fax: 802.878.1776

Email: hti@haemtech.com

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DOMAIN STRUCTURE OF PROTEIN C The domain structure of protein C is represented, where: GLA = region containing γ-carboxyglutamic acid residues, EGF = region containing sequences homologous to human epidermal growth factor, AP = activation peptide released upon conversion of the zymogen to the active serine protease, CATALYTIC DOMAIN = region containing the serine protease catalytic triad. The arrow indicates the site which is proteolytically cleaved by thrombin during activation of the zymogen.

The vitamin K-dependent zymogen, protein C, is synthesized in the liver as a single chain polypeptide and is subsequently converted to a disulfide linked heterodimer, by removal of a dipeptide (Lys-146 and Arg-147) from the precursor molecule (1,2). Trace quantities of the single chain form have been observed in plasma. The light chain, which is responsible for the calcium dependent binding of protein C to phospholipid vesicles, contains 11 γ-carboxyglutamic acid (gla) residues, 1 b-hydroxyaspartic acid residue, and 2 epidermal growth factor (EGF) homology domains. The serine protease catalytic triad is located in the heavy chain. Human protein C is susceptible to proteolytic cleavage of a peptide (Mr=3000) from the COOH-terminal end of the heavy chain, yielding an altered form referred to as β-protein C. No functional distinction between α- and β-protein C has been observed. A single cleavage at Arg-12 (Arg-14 in bovine) of the heavy chain of human protein C converts the zymogen into the serine protease, activated protein C. This cleavage is catalyzed by a complex between α-thrombin and the endothelial cell surface protein thrombomodulin. In contrast to the other vitamin K dependent coagulation factors, activated protein C functions as an anticoagulant by catalyzing the proteolytic inactivation of factors Va and VIIIa. APC also contributes to the fibrinolytic response by complex formation with plasminogen activator inhibitors. 

Bovine protein C is prepared from fresh citrated bovine plasma by a modification of the Walker procedure (3), as described by Haley et al. (4). Human protein C is prepared from fresh frozen citrated human plasma using a combination of immunoaffinity chromatography (5), and conventional techniques (4,9). Protein C is provided in 50% (vol/vol) glycerol/H₂O and should be stored at -20^oC. Purity is determined by SDS-PAGE analysis and activity is measured using a chromogenic substrate based assay.  

Properties of Protein C

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References 

1. Esmon, C.T., Progress in Thromb. and Hemosts., 10, 25 (1984). 
2. Stenflo, J., Semin. in Thromb. and Hemostas., 10, 109 (1984). 
3. Walker, F.J., et al., Biochim. Biophys. Acta, 571, 333 (1979). 
4. Haley, P.E., et al., J. Biol. Chem., 264, 16303 (1989). 
5. Jenny, R.J., et al., Prep. Biochem., 16, 227 (1986). 
6. Griffen, J.H., et al., Blood, 60, 261 (1982). 
7. Kisiel, W., et al., Methods Enzymol., 80, 320 (1981). 
8. Discipio, R.G., et al., Biochemistry, 18, 899 (1979). 
9. Bajaj, S.P., et al., Prep. Biochem., 11, 397 (1981). 

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