Thromb Haemost 2000; 83(02): 253-261
DOI: 10.1055/s-0037-1613796
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Oxidation of Human α-Thrombin by the Myeloperoxidase-H2O2-chloride System: Structural and Functional Effects

Raimondo De Cristofaro
1   From the Hemostasis Research Center, Department of Internal Medicine, Catholic University School of Medicine, Rome, Italy
,
Raffaele Landolfi
1   From the Hemostasis Research Center, Department of Internal Medicine, Catholic University School of Medicine, Rome, Italy
› Author Affiliations
Further Information

Publication History

Received 17 June 1999

Accepted after resubmission 22 October 1999

Publication Date:
11 December 2017 (online)

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Summary

The myeloperoxidase-H2O2-chloride system (MPOS) is exploited by white blood cells to generate reactive oxygen species in many processes involved in the pathogenesis of inflammation and atherothrombosis. This study investigated the biochemical and functional effects of α-thrombin oxidation by MPOS. This system, in the presence of 100 µM L-tyrosine, caused in the thrombin molecule loss of tryptophan and lysine residues and formation of dityrosine, chloramine and carbonyl groups. The same changes could be directly induced by thrombin incubation with reagent HOCl, but not with H2O2 alone. Exposure to either MPOS or HOCl caused major functional abnormalities in human α-thrombin. The interaction of oxidized (ox-)thrombin with Protein C and antithrombin III-heparin complex were most sensitive to oxidation, being the kcat/Km value for Protein C hydrolysis roughly reduced 13-fold and the affinity for the antithrombin III-heparin complex decreased approximately 15-fold. Ox-thrombin interaction with small synthetic peptides showed several changes, arising from a perturbation of the S2-S3 specificity of the enzyme. Ox-thrombin was also characterized by a 5-fold decrease of the kcat/Km value for both fibrinopeptide A and B release from fibrinogen, a 5.8-fold increase of the EC50 value for platelet activation and a 2-fold decrease of binding affinity for thrombomodulin. The above results indicate a high sensitivity of thrombin to oxidative modifications by myeloperoxidase. Perturbed interactions with Protein C and the heparin-ATIII complex were the most relevant functional abnormalities of ox-thrombin.

Abbreviations: DNPH: 2,4-dinitrophenylhydrazine; FpA: fibrinopeptide A; FpB: fibrinopeptide B; FRS: Fibrinogen recognition Site; GpIb: Glycoprotein Ib; HBS: Heparin Binding Site; MPO: myeloperoxidase; MPOS: Myeloperoxidase System; Pip: Pipecolynic acid; PMN: polymorphonuclear cells; pNA: para-nitroaniline; PPACK: Phenylalanine-Proline-Arginine-Chloromethyl-Ketone; TM: Thrombomodulin; TNB: 5-thio-2-nitrobenzoic acid; TPCK: N-tosyl-L-Phenylalanine-Chloromethyl-Ketone. Thrombin residues are numbered according to the chymotrypsin numbering system (31).