Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.7 (plasmin)
 9,023 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

During digestion of highly purified bovine factor VIII or neuraminidase-treated human factor VIII by plasmin the procoagulant activity is destroyed more rapidly than the aggregating activity. At an intermediate stage, fragments are transiently formed, which inhibit platelet aggregation by the respective undigested materials, but without corssed inhibition. During proteolysis by plasmin, human factor VIII retains antigenic and restocetin cofactor properties. Contrary to previous observations obtained with less purified preparations, plasmin digest of human or bovine factor VIII do not inhibit ADP-induced platelet aggregation. Thrombin and reptilase do not modify the aggragating activities of bovine and neuraminidase-treated human factor VIII.
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PMID:Factor VIII and human platelet aggregation. IV. Effect of proteolytic enzymes on platelet aggregation by factor VIII. 13 76

Dialysable peptides (M. W. less than 12,000) were obtained by plasmin digests of purified bovine fibrinogen. The biological effects of these peptides were studied in rats in three different test systems: ADP-induced platelet aggregation, isolated atria contractility and vascular permeability. The effects induced by the peptides were: inhibition of ADP-induced platelet aggregation, increase in the frequency of isolated atria contractions and local increase in vascular permeability. All these activities were concentration dependent. Six micrograms of the peptides were still effective in increasing vascular permeability; in the in vitro systems the smallest effective dose ranged between 165 and 650 mug/ml. Following elution through a Sephadex G-25 gel with bidistilled water, four fractions were obtained. The second fraction (M.W. about 5,000) was the most active, followed by the first and then the third one; the fourth fraction was inactive. These data suggest that local accumulation of peptides in vivo may be of clinical relevancy.
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PMID:Biological properties of dialysable peptides derived from plasmin digestion of bovine fibrinogen preparations. 13 56

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

Aggregation induced in human platelets by thrombin (TH), collagen (COLL) or the Ca++ ionophore, A23187, was blocked by dibucaine and tetracaine. COLL-induced aggregation was blocked at lower concentrations of anesthetics (0.01-0.5 mM) than TH- or A23187-induced aggregation (0.2-2.0 mM). The rate and magnitude of the release of adenosine diphosphate, Ca++ and serotonin was also decreased by anesthetics. Secretion due to COLL, but not to TH, required extracellular Ca++ and was accompanied by increased uptake of 45Ca which was inhibited by local anesthetics. A23187-induced secretion was partially dependent upon external Ca++ and was accompanied by increased 45Ca uptake. Anesthetics increased 45Ca uptake when added before, but not after, A23187. This effect can be explained by postulating that the anesthetics prevent the release of an internal pool of Ca++, thereby affecting the Ca++ gradient between platelet cytoplasm and extracellular fluid. Platelets degramulated, but not aggregated, by exposure to TH in the presence of ethylene glycol bis(beta--aminoethyl ether)-N, N'-tetraacetic acid and plasmin were isolated by sepharose gel filtration. Such platelets did not aggregate with COLL or TH, but did aggregate with A23187-an effect blocked by local anesthetics. Thus platelet aggregation and secretion are independent Ca++-requiring processes, each of which is inhibitable by local anesthetics, presumable by blocking Ca++ influx or the mobilization of intracellular Ca++ stores.
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PMID:An analysis of the mechanism of local anesthetic inhibition of platelet aggregation and secretion. 77 86

The presence of human fibrinogen in suspensions of washed human platelets is a requirement for ADP-induced platelet aggregation. Digestion of fibrinogen with plasmin destroys this function of the protein. The high solubility fraction of Kabi fibrinogen, fragment X (stage 1) and framgent X (stage 2), are two, eight, and ten times, respectively, less potent in promoting ADP-induced platelet aggregation, as compared with intact fibrinogen. Fragments Y and D and the mixture of reduced and carboxymethylated chains of human fibrinogen do not support ADP-induced platelet aggregation at all. SDS polyacrylamide gel electrophoresis of nonreduced and reduced fibrinogen and its derivatives indicates that the intact fibrinogen molecule is essential for ADP-induced platelet aggregation. It is suggested that the carboxy-terminal part of the Aalpha chain and possibly also the amino-terminal part of the Bbeta chain are required for the platelet aggregation-promoting function of fibrinogen.
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PMID:Significance of the intact polypeptide chains of human fibrinogen in ADP-induced platelet aggregation. 84 21

Defective ADP-induced aggregation was observed in in vitro streptokinases(SK)-treated normal platelet-rich plasma. Classic haemophilia and normal platelet poor plasma (PPP) treated with SK inhibit the aggregation of washed platelets; plasmin-treated normal human serum also shows an inhibitory effect on platelet aggregation. However, SK-treated von Willebrand plasmas do not inhibit the aggregation of washed platelets. This confirms the fact that the anti-aggregating effect is mainly linked to the digested factor VIII) but not to the digested fibrinogen. Defective ristocetin-induced platelet aggregation has also been observed in SK-treated plasmas. The presence of normal PPP does not modify the inhibition of the ADP-induced aggregation of washed platelets in SK-treated PPP. However, it does correct the ristocetin-induced aggregation. These results suggest that the inhibition of the ADP-induced aggregation is caused by the factor VIII degradation products, while the inhibition of the ristocetin-induced aggregation appears because of a defective von Willebrand activity of the factor VIII molecule.
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PMID:Inhibition of human platelet aggregation by the proteolytic effect of streptokinase. Role of the human factor-VIII-related protein. 108 12

The mechanisms by which thrombolytic agents affect platelet function are not yet elucidated. The aim of the present study was to investigate the effects of plasmin, generated by thrombolytic agents in plasma, on platelet glycoproteins (GP) Ib and IIb/IIIa. Platelet-rich plasma was incubated with pharmacological amounts of streptokinase, anistreplase and tissue-type plasminogen activator and the platelet surface GP's were investigated with a panel of monoclonal antibodies using flow cytometry. As assessed from the mean fluorescence intensity of incubated and control platelets, no significant changes in the binding of antibodies to GP Ib and GP IIb/IIIa were found. The functional integrity of these glycoproteins was severely impaired by treatment with the thrombolytic agents, as shown by significant inhibition of ADP- and ristocetin-induced platelet aggregation. Experiments with purified plasmin and washed platelets indicated significant degradation of GP IIb/IIIa and upregulation of GP Ib, which is in agreement with previous findings. In addition, platelet activation by plasmin was shown using two monoclonal antibodies to activation-specific antigens. We conclude that degradation of platelet GP's by plasmin offers no likely explanation for the defect in platelet function, which is induced by thrombolytic agents in platelet-rich plasma.
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PMID:Interactions between thrombolytic agents and platelets: effects of plasmin on platelet glycoproteins Ib and IIb/IIIa. 144 May 36

The success of plasminogen activators in recanalizing occluded coronary arteries may be influenced by their effect on blood platelets; however, some previous studies have shown platelet activation by plasmin and thrombolytic agents while others have shown an inhibitory effect. Moreover, it has not been determined whether these effects reflect an alteration of intracellular signal transduction, fibrinogenolysis, degradation of adhesive protein receptors, or a combination of these events. To distinguish among these possibilities, the increase of cytoplasmic [Ca2+] [( Ca2+]i), which is an intracellular marker of platelet activation that precedes fibrinogen binding to the surface of activated platelets, was measured along with aggregation and release of 5-hydroxytryptamine (5-HT) in washed human platelets incubated with plasmin or recombinant tissue-type plasminogen activator (rt-PA). Plasmin (0.1 to 1.0 CU/mL) induced a prompt, concentration-dependent [Ca2+]i increase when added to platelets, but subsequently inhibited the [Ca2+]i increase in response to thrombin or the endoperoxide analog U44069. Platelet aggregation accompanied the [Ca2+]i increase if the platelets were stirred, while the aggregation of platelets unstirred during plasmin incubation was inhibited upon agonist addition and resumption of stirring. The release of 5-HT paralleled the [Ca2+]i increase induced by plasmin and was also inhibited after the subsequent addition of a second agonist. The effects of rt-PA, added with plasminogen (100 micrograms/mL), were similar to those of plasmin, and could be accounted for by the concentration of plasmin generated. The ADP scavengers apyrase and CP/CK each prevented the [Ca2+]i increase, and aggregation caused by plasmin or rt-PA, and also prevented their inhibitory effects on thrombin-induced activation. Thus, plasmin and rt-PA initially activate platelets, inducing a [Ca2+]i increase, and, if the platelets are stirred, aggregation. Such activation is followed by subsequent inhibition of cellular activation by a second agonist; the inhibitory effect is in proportion to the degree of initial activation, and ADP is an important cofactor in both processes. These platelet effects occur at rt-PA concentrations achievable clinically, and may affect the success of therapy with thrombolytic and adjunctive agents.
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PMID:Platelet activation and subsequent inhibition by plasmin and recombinant tissue-type plasminogen activator. 153 Aug 14

Plasmin is known to activate platelets. However, it is not clear whether plasminogen activators as used in thrombolytic therapy can aggregate platelets and how this relates to the ability of each activator to convert plasminogen to plasmin. Urokinase (UK) and streptokinase (SK) activated purified plasminogen (2 microM) in a concentration-dependent manner. The rates of aggregation of washed platelets by the above plasminogen activators and plasminogen were similar to the extent of activation of plasminogen to plasmin in the absence of platelets. UK or SK (0.2 microM) and plasminogen (2 microM) aggregated platelets modified by an ADP affinity analog, 5'-p-fluorosulfonylbenzoyladenosine (FSBA), and cleaved aggregin, a putative ADP receptor, in [3H]FSBA-modified platelets. These results suggest that the effect was independent of ADP. In contrast, incubation mixtures containing only plasminogen (2 microM) and single chain tissue plasminogen activator (sc-tPA) (less than or equal to 0.12 microM) neither activated the zymogen to an appreciable extent nor aggregated platelets. But, in the presence of fibrin(ogen) fragments (tPA-stimulator), a mixture of plasminogen and sc-tPA aggregated unmodified and FSBA-modified platelets, and cleaved aggregin. The results imply that platelets, in the presence of t-PA stimulator, potentiate activation of plasminogen to plasmin by t-PA, as previously reported. P1, Phe-Gln-Val-Val-Cys-(NpyS)-Gly-NH2, (NpyS = 3-nitro-2-thiopyridine), a synthetic hexapeptide capable of binding to and inhibiting calpain, has been shown to inhibit platelet aggregation induced by purified plasmin. P1 inhibited platelet aggregation by plasminogen and any of the three plasminogen activators. Our results show that at plasma concentrations of plasminogen and at levels of UK and SK attained after infusion of these agents during thrombolysis, these mixtures can cause maximum aggregation which may contribute to reocclusion and stenosis following infarct therapy. P1 can effectively inhibit platelet aggregation under such conditions.
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PMID:Aggregation of washed platelets by plasminogen and plasminogen activators is mediated by plasmin and is inhibited by a synthetic peptide disulfide. 153 63

Both augmentation of thrombin activity and activation of platelets have been reported to accompany administration of plasminogen activators in vivo. To determine whether the platelet activation is a consequence or a cause of the procoagulant effects, we assessed the effects of t-PA on spontaneous activation and aggregation of platelets and on clotting in recalcified human whole blood. Spontaneous activation of platelets occurred in the stirred samples 8.9 +/- 2 minutes (n = 5) after recalcification. Aggregation and clotting followed immediately afterward. Activation, aggregation and clotting were accelerated in a dose-dependent manner by 3 minutes of preincubation with t-PA (2-30 micrograms/ml) before recalcification. The procoagulant effect of t-PA (5 micrograms/ml) was abolished by concomitant incubation with hirudin (0.5 nM) or aprotinin (200 KIU/ml) consistent with the hypothesis of plasmin-mediated evolution of thrombin being responsible for the procoagulant effect. However, platelets could be activated independently by other agonists (collagen, 3 micrograms/ml; and ADP, 25 microM) in the presence of hirudin. Despite the procoagulant effect of t-PA, aggregation to collagen (2-5 micrograms/ml) and PAF (0.9 microM) was diminished in samples incubated with t-PA for 30 minutes (37 degrees C). Fibrinogen degradation products elaborated during this interval (25.6 micrograms/ml; n = 3) were responsible for this anti-aggregatory effect. The results indicate that platelet activation in recalcified whole blood depends on procoagulant effects of t-PA.
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PMID:The dependence of activation of platelets by a plasminogen activator on the evolution of thrombin activity. 172 1


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