Multiple active forms of thrombin. IV. Relative activities of meizothrombins

Journal Article · Mon Jun 25 00:00:00 EDT 1990 · Journal of Biological Chemistry; (USA)

OSTI ID:6718609

Doyle, M F; Mann, K G ^[1]

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1. Univ. of Vermont College of Medicine, Burlington (USA)

The prothrombin activation intermediates meizothrombin and meizothrombin(desF1) (meizothrombin that has been autoproteolyzed to remove fragment 1) have been obtained in a relatively pure, active form with minimal autolysis, making them suitable for enzymatic characterization. When compared at equimolar concentrations, alpha-thrombin, fragment 1.2+ alpha-thrombin, meizothrombin(desF1), and meizothrombin have approximately 100, 100, 10, and 1% activity, respectively, toward the macromolecular substrates factor V, fibrinogen, and platelets. The difference in activity of these four enzymes cannot be attributed to alterations in the catalytic triad, as all four enzymes have nearly identical catalytic efficiency toward the chromogenic substrate S2238. Further, the ability of meizothrombin and meizothrombin(desF1) to activate protein C was 75% of the activity exhibited by alpha-thrombin or fragment 1.2+ alpha-thrombin. All four enzymes bind to thrombomodulin, as judged by the enhanced rate of protein C activation upon preincubation of the enzymes with thrombomodulin. The extent of rate enhancement varied, with meizothrombin/thrombomodulin exhibiting only 50% of the alpha-thrombin/thrombomodulin rate. This difference in rate is not due to a decreased affinity of the meizothrombin for thrombomodulin since the apparent dissociation constants for the alpha-thrombin-thrombomodulin complex and the meizothrombin-thrombomodulin complex are virtually identical. The difference in the observed rate is due in part to the higher Km for protein C exhibited by the meizothrombin-thrombomodulin complex. Incubation of the thrombomodulin-enzyme complex with phospholipid vesicles caused an increase in the protein C activation rates. The kinetic constants for protein C activation in the presence of phospholipid are virtually identical for these enzyme-thrombomodulin complexes.

• OSTI ID: 6718609
• Journal Information: Journal of Biological Chemistry; (USA), Vol. 265:18; ISSN 0021-9258
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
PEPTIDE HYDROLASES
ENZYME ACTIVITY
PROTHROMBIN
THROMBIN
AUTORADIOGRAPHY
BIOCHEMICAL REACTION KINETICS
CATTLE
IODINE ISOTOPES
MOLECULAR WEIGHT
PHOSPHOLIPIDS
PRECURSOR
ANIMALS
BLOOD COAGULATION FACTORS
COAGULANTS
DOMESTIC ANIMALS
DRUGS
ENZYMES
ESTERS
HEMATOLOGIC AGENTS
HEMOSTATICS
HYDROLASES
ISOTOPES
KINETICS
LIPIDS
MAMMALS
ORGANIC COMPOUNDS
ORGANIC PHOSPHORUS COMPOUNDS
PROTEINS
REACTION KINETICS
RUMINANTS
SERINE PROTEINASES
VERTEBRATES
550201* - Biochemistry- Tracer Techniques