Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.68 (tissue plasminogen activator)
 11,311 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two fluorogenic peptide amides have been synthesized, i.e. BOC-L-valyl-glycyl-L-arginine 2-naphthylamide (I) and L-valyl-glycyl-L-arginine 2-naphthylamide (II). The kinetic parameters of plasmin, urokinase and human uterine tissue plasminogen activator on substrates I and II have been determined. Quite unexpectedly, the tissue activator appeared to require for its activity a blocked amino terminus on the substrate. This was further corroborated with other synthetic substrates. Plasmin and urokinase did not show this requirement.
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PMID:Fluorogenic substrates for sensitive and differential estimation of urokinase and tissue plasminogen activator. 65 77

Plasmin inhibition by alpha 2-antiplasmin (alpha 2AP) is regulated by the vascular components fibrin(ogen) fragments, plasminogen and lipoprotein (a). Kinetic analysis demonstrates that CNBr-derived fibrinogen fragments completely protect plasmin from alpha 2AP. Plasminogen and 6-aminohexanoic acid decrease the rate of inhibition by 5- and 10-fold respectively. These studies show that CNBr-derived fibrinogen fragments and 6-aminohexanoic acid bind plasmin kringle(s) with binding constants of 2 micrograms/ml and 120 microM respectively, and that plasminogen binds to alpha 2AP with an affinity of 0.5 nM. The unmodulated inhibition is not effected by the presence of lipoprotein (a), but in the presence of protective CNBr-derived fibrinogen fragments the rate of inhibition is increased by the presence of the lipoprotein. The kinetics demonstrate that lipoprotein (a) binds to CNBr-derived fibrinogen fragments with an affinity of 4 nM, displacing plasmin from the protective surface. In addition, tissue-type plasminogen activator and trypsin inhibition by alpha 2AP is not slowed by the presence of CNBr-derived fibrinogen fragments or plasminogen (Pg), respectively. These kinetics suggest that the initial reversible interaction between plasmin and alpha 2AP is mediated by binding of the inhibitor to the kringle 1 domain of plasmin, with a reversible inhibition constant (Ki) of 5.0 x 10(-10) M. Under conditions where this kringle-inhibitor interaction is blocked, the reversible inhibition still occurs between the plasmin and alpha 2AP, but the initial Ki is increased to 5.0 x 10(-9) M. These data suggest that, in the circulation, plasmin inhibition by alpha 2AP may be down-regulated by fibrin, fibrin(ogen) fragments and Pg, but up-regulated by lipoprotein (a) in the presence of fibrin or fibrin(ogen) fragments. The lipoprotein (a)-mediated promotion of plasmin inhibition may provide an additional mechanism by which the lipoprotein impairs fibrinolysis and promotes atherosclerosis.
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PMID:Lipoprotein (a) promotes plasmin inhibition by alpha 2-antiplasmin. 138 85

Plasmin inhibited the biosynthesis of tissue-type plasminogen activator (tPA) antigen by human umbilical vein endothelial cells (HUVEC) in a dose-dependent manner. The amount of tPA antigen found in the 24-h conditioned medium of cells treated with 100 nM plasmin for 1 h was 20-30% of that in the control group. However, in contrast to tPA, such treatment led to a 3-fold increase in plasminogen activator inhibitor (PAI) activity, whereas the amount of PAI type 1 antigen was unchanged. The effects of plasmin on HUVEC were binding- and catalytic activity-dependent and were specifically blocked by epsilon-aminocaproic acid. Microplasmin, which has no kringle domains, was less effective in reducing tPA antigen biosynthesis or enhancing PAI activity in HUVEC. Kringle domains of plasmin affected neither tPA antigen nor PAI activity of the cells. Other proteases including chymotrypsin, trypsin, and collagenase at comparable concentrations did not have a significant effect on the biosynthesis of tPA antigen or PAI activity of HUVEC. Thrombin stimulated the biosynthesis of tPA and PAI-1 antigens by HUVEC. Thrombin also stimulated an increase in the protein kinase activity in HUVEC, whereas plasmin inhibited the protein kinase activity of the cells. It is possible that plasmin regulates the biosynthesis of tPA in HUVEC through the signal transduction pathway involving protein kinase.
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PMID:Plasmin and the regulation of tissue-type plasminogen activator biosynthesis in human endothelial cells. 138 68

The generation of the proteolytic enzyme plasmin from its inactive precursor plasminogen, mediated by so called plasminogen activators, is the essential step in thrombolytic therapy. Plasmin is responsible for the degradation of the insoluble fibrin, the major component of a thrombus, to soluble fibrin degradation products. So far, the use of the more recently developed thrombolytic agents single-chain urokinase-type plasminogen activator (scu-PA) and tissue-type plasminogen activator (t-PA) were disappointing, mainly due to some of their negative properties in vivo, i.e., rapid inhibition and/or hepatic clearance. Besides some background information on the haemostatic balance; t-PA and scu-PA structure; and mechanisms of action, we here review some reported attempts to improve on these agents for thrombolytic therapy following various strategies. One of the more potential strategies, antibody-targeted thrombolytic therapy using bispecific monoclonal antibodies, is discussed somewhat more extensively, as are the several procedures that can be followed for bispecific antibody preparation.
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PMID:The potential improvement of thrombolytic therapy by targeting with bispecific monoclonal antibodies: why they are used and how they are made. 141 66

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

Thrombospondin is a multifunctional glycoprotein of platelet alpha-granules and a variety of growing cells. We demonstrate that thrombospondin is a slow tight-binding inhibitor of plasmin as determined by loss of amidolytic activity, loss of ability to cleave fibrinogen, and decreased lysis zones in fibrin plate assays. Stoichiometric titrations indicate that approximately 1 mol of plasmin interacts with 1 mol of thrombospondin, an unexpected result considering the trimeric nature of thrombospondin. Plasmin in a complex with streptokinase or bound to epsilon-aminocaproic acid is protected from inhibition by thrombospondin, thereby implicating the lysine-binding kringle domains of plasmin in the inhibition process. Thrombospondin also inhibits urokinase plasminogen activator, but more slowly than plasmin, stimulates the amidolytic activity of tissue plasminogen activator, and has no effect on the amidolytic activity of alpha-thrombin or factor Xa. These results, therefore, identify thrombospondin as a new type of serine proteinase inhibitor and potentially important regulator of fibrinolysis.
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PMID:Thrombospondin is a slow tight-binding inhibitor of plasmin. 153 Oct 22

Osteoblasts produce proteolytic enzymes and their production is regulated by osteotropic agents. It has been suggested that these proteases play a role in bone resorption by removing the superficial collagenous layer from the bone matrix and indirectly inducing migration of osteoclast precursors towards the bone matrix. We examined the effect of the plasminogen activator tPA on osteoclastic resorption using 17-day-old mouse embryonic long bone explants representing different stages of osteoclast development, that is, radii containing already mature osteoclasts and metacarpals containing no mature osteoclasts but only osteoclast precursors/progenitors which are still confined to the periosteum. Tissue type PA stimulated osteoclastic resorption (measured as 45Ca-release) in 17-day-old fetal metacarpals but not in radii of the same animal. Blocking the enzymatic activity of tPA did not inhibit its effect on osteoclastic resorption. Plasmin, the direct product of PA enzymatic activity, did not induce osteoclastic resorption. However, a tPA-mutant missing the growth-factor-like domain of the molecule, failed to stimulate 45Ca-release from the metacarpals. In addition, in both systems tPA and transforming growth factor alpha had similar effects on osteoclastic resorption. The finding that tPA stimulated 45Ca-release only in the metacarpals suggests that tPA has an effect on osteoclast formation rather than on the activity of already mature osteoclasts. Under the experimental conditions used this effect seems to be mediated by the growth factor domain of tPA rather than by the enzymatic activity of the molecule.
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PMID:The effect of tissue type plasminogen activator (tPA) on osteoclastic resorption in embryonic mouse long bone explants: a possible role for the growth factor domain of tPA. 153 5

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

Fibrinolytic therapy has an expanding role in the treatment of many thromboembolic disorders. Four fibrinolytic drugs are currently marketed: streptokinase, anisoylated plasminogen-streptokinase activator complex, urokinase, and recombinant human tissue-type plasminogen activator. All 4 of these drugs activate the fibrinolytic system by converting plasminogen to the active enzyme, plasmin. Plasmin present in the confines of a thrombus degrades fibrin and dissolves the thrombus. Plasmin free in the circulation degrades fibrinogen and other coagulation factors. All 4 of the currently available fibrinolytic agents are capable of initiating thrombus dissolution and, at doses currently recommended, cause degradation of fibrinogen and predispose to bleeding complications. Differences in the mechanisms of plasminogen activation among the available agents provide a theoretical basis for postulating the superiority of one agent over another in clinical practice. However, the relative roles of these agents in treatment of thromboembolic disorders depend on the outcome of properly designed and executed clinical trials.
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PMID:Pharmacology of fibrinolysis. 155 84

Release of tissue plasminogen activator (t-PA) and its interaction with plasma protease inhibitors were studied in two patients with massive defibrination, one after electroshock and soft tissue injury and the other after complicated labor; both had very severe hemorrhage. Large quantities of free t-PA were present in the circulation for several hours. Complexes of t-PA with plasminogen activator inhibitor 1 (PAI-1), alpha 2-macroglobulin and C1-inhibitor were also observed. PAI-1 antigen rose dramatically in both patients, and complexes of t-PA with PAI-1 rose rapidly during the period of observation. In contrast, the complexes of t-PA with alpha 2-macroglobulin and C1-inhibitor, present initially, persisted for short periods only and disappeared when free t-PA disappeared from the circulation. Plasmin was generated initially, as indicated by the presence of plasmin-alpha 2-antiplasmin complexes. Plasma concentrations of alpha 2-macroglobulin, C1-inhibitor, antithrombin III, and alpha 2-antiplasmin were severely depleted initially, but rapidly returned to normal. The observations demonstrate that there is a major release of t-PA in such defibrinating patients, that there is a role for protease inhibitors other than PAI-1 in the regulation of endogenous t-PA, and indicate the great rapidity with which such free t-PA is complexed and cleared.
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PMID:Complexing of tissue plasminogen activator with PAI-1, alpha 2-macroglobulin, and C1-inhibitor: studies in patients with defibrination and a fibrinolytic state after electroshock or complicated labor. 168 22


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