Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.4.21.5 (thrombin)
33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Thrombin converts fibrinogen to fibrin monomer by cleaving fibrinopeptides A and B (FPA and FPB) from the amino terminal ends of the A (alpha) and B (beta) chains. A radioimmunoassay capable of measuring the A peptide in human blood as an index of thrombin action in vivo has been described previously. This paper describes the development of a radioimmunoassay for FPB and the use of both assays in the demonstration of distinctive patterns of cleavage of the amino terminal ends of the A (alha) and B (beta) chains of fibrinogen by various enzymes. Antisera were raised in rabbits to a synthetic analogue of FPB coupled to bovine serum albumin. FPB analogue was couple to desaminotyrosine and radiolabeled with 125I by the chloramine-T technique. The radiolabeled peptide was bound by the antiserum, and binding was inhibited by synthetic or native FPB. Unbound tracer was separated from bound tracer by charcoal adsorption. The senistivity of the assay was such that 50% inhibition of binding of the tracer was caused by 1.25 ng of the native FPB. Fibrinogen was treated with thrombin, plasmin, trypsin, Reptilase, and an extract of the venom from Ancistrodon contortrix contortrix (ACC). After ethanol precipitation and centrifugation, dialysates of enzymatically altered fibrinogen were assayed for FPA and FPB. The action of thrombin on fibrinogen resulted in a rapid release of FPA and a slower release of FPB. Plasmin cleaved a segment(s) of the B (beta) chain which included FPB but cleaved no detectable FPA-containing material for the first 2 h of incubation. In the case of plasmin-treated fibrinogen, the dialysates had been further treated with thrombin before being assayed for FPA and FPB. Trypsin rapidly cleaved both peptides, the B before the A. Reptilase cleaved only FPA in 24 h. ACC cleaved FPB at a rapid rate, with a slowere cleavage of FPA. The distinctive cleavage patterns produced by the serine proteases may be useful in interpreting the levels of FPA and FPB measured in human blood and in studying the generation of FPA and FPB in clinical blood samples.
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PMID:Radioimmunoassay of human fibrinopeptide B and kinetics of fibrinopeptide cleavage by different enzymes. 5 Mar 28

The effects of plasmin treatment upon washed human platelets were studied in an attempt to elucidate the mechanisms underlying thrombin-induced platelet aggregation. At calcium concentrations of 10-20 muM, PLASMIN (0.2 CTA U/ml) inhibited thrombin-induced aggregation almost completely, but did not diminish the thrombin-induced release of adenine nucleotides, 5-hydroxytryptamine, or calcium. Increasing the calcium concentration partially antagonized plasmin's inhibition of aggregation. Studies utilizing calcium chelators and the Kunitz soybean trypsin inhibitor (SBTI) as a plasmin inhibitor indicated that in order to achieve maximal block of aggregation, plasmin must act upon a substrate made fully available only after an initial thrombin-platelet interaction has taken place. Moreover, the time course of this inhibition parallels the time course of the thrombin-induced release reaction. Plasmin inhibition of aggregation could not be mimicked by exposing the platelets to proteolytic digests of fibrinogen at concentrations as high as 17% total platelet protein. Nor could inhibitory activity be recovered from supernatants of plasmin-treated platelets, upon centrifugation and treatment with SBTI. With the use of a "cold initiation" technique, the release by thrombin of 46.7 plus or minus 6.7 (mean plus or minus SEM) mu-g of fibrinogen immunological equivalents per mg platelet protein could be demonstrated. Platelets in which thrombin-induced aggregation was abolished by plasmin treatment (and the plasmin subsequently inactivated by STBI) aggregated normally upon addition of as little as 10 mu-g human plasma fibrinogen per mg platelet protein. It is concluded that plasmin inhibition of aggregation most likely results from its attack upon a protein that is released or becomes fully available subsequent to interaction of thrombin with a platelet receptor mediating release. The results of this study are consistent with a cofactor role for fibrinogen in the aggregation of human platelets by thrombin.
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PMID:Plasmin inhibition of thrombin-induced platelet aggregation. 12 75

The inhibition of plasmin, (EC 3.4.21.7), thrombin (EC 3.4.21.5), trypsin (EC 3.4.21.4) and chymotrypsin (EC 3.4.21.1) by antiplasmin, the recently described fast-reacting plasmin inhibitor of human plasma, was studied. To determine the quantitative importance of antiplasmin relative to the other plasma protease inhibitors, enzyme inhibition assays were performed on whole plasma and on plasma specifically depleted in antiplasmin, after addition of excess enzyme. Plasmin was the only enzyme for which the inhibitory capacity of antiplasmin-depleted plasma was lower than that of normal plasma. To determine the affinity of the enzymes for antiplasmin, as compared to the other inhibitors, various amounts of enzymes were added to normal plasma and the formation of enzyme-antiplasmin complexes studied by crossed immunoelectrophoresis using specific antisera against antiplasmin. Plasmin and trypsin, but not thrombin or chymotrypsin formed complexes with antiplasmin. It is concluded that antiplasmin is the only fast-reacting plasmin inhibitor of human plasma. It is also a fast-reacting inhibitor of trypsin but only accounts for a very small part of the fast-reacting trypsin-inhibitory activity of plasma. This can be explained by the low concentration of antiplasmin (1 muM) in normal plasma, compared to the other inhibitors (e.g. alpha1-antitrypsin: 40-80 muM).
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PMID:The interaction in human plasma of antiplasmin, the fast-reacting plasmin inhibitor, with plasmin, thrombin, trypsin and chymotrypsin. 14 66

Proteolysis of human cross-linked fibrin by plasmin results in the formation of a DD . E complex, and Fragments DD and E as the major degradation products. Three species of Fragment E, which differ both in molecular weights (E1, Mr = 60,000; E2, Mr = 55,000; E3, Mr = 50,000) and in charge, have been isolated from a digest of cross-linked fibrin. Each Fragment E species reacts with monospecific anti-E antiserum. Fragments E1 and E2 bind with Fragment DD to form a DD . E complex but Fragment E3 is inactive. This binding is specific since these Fragments E do not bind to fibrinogen or to degradation products of fibrinogen or of noncross-linked fibrin. Fragments E1 and E2 incubated with plasmin are degraded to Fragment E3, suggesting that the three species represent sequential degradation products. Plasmin-treated Fragments E1 and E2 no longer bind with Fragment DD; therefore, it appears that the peptides cleaved from Fragment E2 by plasmin contain or modify the sites responsible for complex formation. On the other hand, Fragment DD binds not only to Fragments E1 and E2, but also to fibrinogen, Fragments X (Stage 1), X (Stage 2), Y, and NH2-terminal disulfide knot, but only after thrombin treatment, suggesting that Fragment DD binds to complementary sites on the NH2-terminal region of fibrinogen which are exposed after thrombin treatment.
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PMID:Binding phenomena of isolated unique plasmic degradation products of human cross-linked fibrin. 15 98

alpha(2)-Plasmin inhibitor (alpha(2)PI) is a recently characterized, fast-reacting plasmin inhibitor in human plasma that appears to play an important role in regulation of in vivo fibrinolysis. We report here a case of complete deficiency of alpha(2)PI in man. The patient, a 25-yr-old Japanese man, had a life-long severe bleeding tendency (hemarthrosis and excessive bleeding after trauma). The following tests were within normal limits: platelet count, bleeding time, thrombin time, prothrombin time, partial thromboplastin time, titers of known clotting factors, platelet glass bead retention, Factor VIII-related antigen, platelet aggregation by ADP, collagen and ristocetin, and clot retraction. Routine liver function tests were also normal. The only abnormal finding was that whole blood clot lysis was extemely rapid and was complete in 4-8 h. The concentration of plasma protease inhibitors, including alpha(2)-macro-globulin, antithrombin III, alpha(1)-antitrypsin, and C1INH, were all normal. The concentration of alpha(2)-PI in the patient's plasma, assayed by immunological methods, was <0.1 mg/100 ml (normal concentration, 6.1+/-0.88 mg/100 ml [mean+/-SE]) and functional assays showed a complete deficiency of alpha(2)PI. Addition of purified alpha(2)PI to the patient's whole blood completely corrected the accelerated fibrinolysis. The patient's parents, four siblings, and four other members of this family were asymptomatic, but the titers of alpha(2)PI in their plasmas were congruent with50% of normal pooled plasma. There were three consanguineous marriages in this family, and the alpha(2)PI deficiency appears to have been inherited as an autosomal recessive trait. We speculate that alpha(2)PI deficiency in this patient has led to uninhibited in vivo fibrinolysis that probably causes the severe hemorrhagic tendency. Thus, this study indicates the important role of alpha(2)PI in hemostasis.
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PMID:Congenital deficiency of alpha 2-plasmin inhibitor associated with severe hemorrhagic tendency. 15 96

alpha 2-Plasmin inhibitor (alpha 2PI) has been recently characterized as a fast-reacting inhibitor of plasmin in human plasma and appears to play an important role in the regulation of fibrinolysis in vivo. We have studied the effect of purified alpha 2PI upon various proteases participating in human blood coagulation and kinin generation. At physiological concentration (50 microgram/ml), alpha 2PI inhibited the clot-promoting and prekallikrein-activating activity of Hageman factor fragments, the amidolytic, kininogenase, and clot-promoting activities of plasma kallikrein, and the clot-promoting properties of activated plasma thromboplastin antecedent (PTA, Factor XIa) and thrombin. alpha 2PI had minimal inhibitory effect on surface-bound activated PTA and activated Stuart factor (Factor Xa). alpha 2PI did not inhibit the activity of activated Christmas factor (Factor IXa) or urinary kallikrein. Heparin (1.5-2.0 units/ml) did not enhance the inhibitory function of alpha 2PI. These results suggest that, like other plasma protease inhibitors, alpha 2PI possesses a broad in vitro spectrum of inhibitory properties.
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PMID:Inhibitory spectrum of alpha 2-plasmin inhibitor. 15 64

Plasmin does not activate factor X into the enzyme--factor Xa. On the contrary, the enzyme inactivates factor X, rendering it incapable of conversion into factor Xa during incubation in 25% sodium citrate. After proteolysis by plasmin the prothrombin preparations contaminated with factor X lose their ability to generate thrombin. This ability is partially restored by an addition of factor X.
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PMID:[Inactivation of factor X by plasmin]. 15 77

Pretreatment of hog high molecular weight renin for 30 min at 37 degrees C with 0.12 unit of either kallikrein or thrombin significantly increased (p less than 0.001) the amount of angiotensin I formed during subsequent incubations with homologous angiotensinogen. However, the thrombin-treated hog renin had 13 times more activity than the kallikrein-treated enzyme. Aprotinin did not inhibit the kallikrein-mediated activation of renin; the results indicated that aprotinin inhibited renin preferentially. Plasmin (0.25 unit) had little effect on the activity of high molecular weight renin. The molecular weight of hog renin on sodium dodecyl sulfate-polyacrylamide gel electrophoresis was not altered after exposure to either kallikrein, thrombin, or plasmin. These results do not exclude the occurrence of a limited proteolytic event or a conformational change beyond the detection of the current method. The data show that the activation of hog high molecular weight renin by thrombin and kallikrein was not associated with the conversion of renin to Mr = 43,000.
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PMID:The effects of kallikrein, plasmin, and thrombin on hog kidney renin. 15 4

The two stages in the activation of human plasminogen by urokinase have been examined kinetically in order to evaluate the significance of each stage in the activation process. The cleavage of the preactivation peptide from the NH2 terminus of native plasminogen (NH2-terminal glutamic acid) is clearly catalyzed by urokinase and is the rate-limiting first step in activation (Stage 1); this reaction is 20-fold slower than the conversion of the intermediate plasminogen (NH2-terminal lysine) to plasmin (Stage 2). Both lysine and its analogoue, epsilon-aminocaproic acid, exert two effects on the activation of native plasminogen. At low concentrations of these agents, activation is greatly accelerated. Analysis of activation in the presence and absence of these agents by sodium dodecyl sulfate gel electrophoresis indicates that the activation pathway is the same in both cases with the formation of a transient intermediate plasminogen; only the kinetics of proteolysis are altered. This enhancement in the rate of activation results solely from acceleration of the Stage 1 reaction; Stage 2 is essentially unaffected at low concentrations. Stage 1 is maximally enhanced (75-fold) at either 0.0025 M epsilon-aminocaproic acid or 0.025 M lysine and occurs 4 times more rapidly than Stage 2, which becomes the rate-limiting step at these concentrations. Plasmin also cleaves the preactivation peptide from native plasminogen and this reaction rate is enhanced by the same concentrations of lysine and epsilon-aminocaproic acid. These data suggest that lysine and epsilon-aminocaproic acid, which are known to bind to plasminogen and significantly alter its conformation, may thereby enhance preactivation peptide cleavage and consequently, plasminogen activation. At high concentrations, both Stages 1 and 2 are similarly inhibited by these agents, which suggests that this effect may be exerted by the direct inhibition of urokinase. The relative rates of preactivation peptide cleavage by the enzymes urokinase, plasmin, thrombin, and ancrod were also determined. Urokinase is 10 times more effective than plasmin in catalyzing this reaction and 1.8 X 10(4) times more effective than thrombin, while ancrod does not exert an effect. No plasmin is formed by either thrombin or ancrod.
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PMID:The importance of the preactivation peptide in the two-stage mechanism of human plasminogen activation. 115 Jun 67

The formation and structure of the complement cytolytic intermediary complex, C5b-7, were studied with the aim of determining the interactive regions of C5, C6, and C7. The structure of human complement component C5 was elucidated by the application of limited proteolysis which generated well characterized major polypeptide fragments of this molecule. Plasmin, thrombin, and kallikrein cleave C5b with greater facility than C5. The most useful cleavage of C5b was effected by plasmin because the fragmentation pattern was similar to the processing of C3b by factors H, I, and kallikrein. Plasmin hydrolyzes peptide bonds within the alpha'-chain of C5b, resulting in a four-chain fragment, C5c (M(r) = 142,000), and a single chain fragment, C5d (M(r) = 43,000). Circular dichroism spectroscopic analyses indicated that C5d is substantially richer in alpha-helical content than is C5c (27 versus 9%). Polyclonal antibodies directed against C5c blocked the interaction of C5b-6 with C7, whereas antibodies directed against C5d inhibited the binding of C5 with C3b. Chemical cross-linking using a cleavable radioiodinated photoreactive reagent revealed that both C6 and C7 associate preferentially with the alpha'-chain of C5b. The reversible interactions of C5 with C6, C7, and major polypeptide fragments derived from these were investigated with solid phase binding assays. The results indicate that the carboxyl-terminal domains of C6 and C7, which have cysteine-rich modules homologous to those found in factors H and I, have the capacity to link specifically with C5.
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PMID:Formation and structure of the C5b-7 complex of the lytic pathway of complement. 138 99


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