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Query: UNIPROT:P00750 (PLA)
 16,800 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The activation of plasminogen by two novel hybrid enzymes, constructed from the A-chain of plasmin and the B-chains of tissue-type plasminogen activator (t-PA) or urokinase, was compared with the activation by the parent enzymes. Basal kinetic constants for 'Lys-plasminogen' (human plasminogen with N-terminal lysine) and 'Glu-plasminogen' (human plasminogen with N-terminal glutamic acid) activation were similar to those of the parent activators. The Km for plasminogen turnover for both hybrid enzymes was considerably decreased in the presence of both soluble fibrin and a mimic, a CNBr digest of fibrinogen. These enhancements and the related apparent negative co-operativity are similar to the behaviour of t-PA itself. The results are discussed with regard to the molecular features involved in the mechanism of fibrin stimulation.
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PMID:Kinetic studies on novel plasminogen activators. Demonstration of fibrin enhancement for hybrid enzymes comprising the A-chain of plasmin (Lys-78) and B-chain of tissue-type plasminogen activator (Ile-276) or urokinase (Ile-159). 213 24

Study has been made of the influence of addition of human NH2 terminal glutamic acid plasminogen (Glu-Plg) or human NH2 terminal lysine plasminogen (Lys-Plg) to normal citrated plasma upon the rate of lysis of fully crosslinked plasma clots in the presence of single or two chain urokinase type plasminogen activator (scu-PA/tcu-PA) or tissue plasminogen activator (t-PA). The specificity of any thrombolytic property was evaluated by measurement of plasma fibrinogen levels. Lys-Plg added to a concentration of 20% of normal plasma plasminogen caused 5 to 6 fold increase in the extent of lysis observed at 6 hours by 100 units/ml of scu-PA and with a small increase in fibrinogenolysis. Glu-Plg added at 20% of normal level had no influence on thrombolysis but at 50% of normal caused increased thrombolysis with rapid depletion of plasma fibrinogen. An apparently synergistic effect of addition of tcu-PA on scu-PA activity was increased by addition of plasminogen (e.g. addition of 20% Lys-Plg increased the lysis rate 4 to 5 fold over the first hour equivalent to an increase of potency of approximately three to four fold). Addition of plasminogen up to double the normal plasma concentration was observed to have no influence on clot lysis in the presence of t-PA. Plasminogen potentiated the rate of lysis by scu-PA/t-PA synergic mixtures with an approximately 1.5 to 1.9 fold increase in potency. Potentiation occurred without increase in the depletion of plasma fibrinogen.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Potentiation by Lys-plasminogen of clot lysis by single or two chain urokinase-type plasminogen activator or tissue-type plasminogen activator. 250 59

The fibrinolytic (fibrin dissolving) properties of several anionic, cationic, nonionic and zwitterionic detergents were assessed in an in vitro fibrin agarose assay. Of the 4 anionic detergents tested, only sodium dodecyl sulfate (SDS) was found to be fibrinolytic. SDS was fibrinolytic either in the absence or presence of factor XIII. Four other cationic detergents were found to possess similar fibrinolytic properties. These cationic detergents were cetyltrimethylammonium bromide (CTAB), mix alkyltrimethyl ammonium bromide (MTAB), hexadecyltrimethylammonium bromide (HTAB) and cetylpyridium chloride (CPC). The nonionic (digitonin, triton X-100/tween 20) and zeitterionic (CHAPS, zeittergent 3-08) detergents were not fibrinolytic. Detergents mediated fibrinolysis, unlike that of tissue type plasminogen activator and urokinase, was independent of the presence of plasminogen. Non-detergents such as polyethylene glycol and highly charged compounds such as poly-1-lysine and poly-1-glutamic acid were not fibrinolytic. Fibrinolytic activity was observed for SDS and the cationic detergents at concentrations ranging from 0.1-10 percent. The effects of these fibrinolytic detergents (SDS, CTAB, MTAB, HTAB and CPC) on clot formation and on pre-formed clots were then assessed, using freshly drawn human venous blood. Incorporation of these detergents into blood inhibited the formation of clots in a concentration dependent manner. The detergents were also able to dissolve pre-formed clots in a similar fashion. SDS was found to be most potent in these properties.
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PMID:Fibrin solubilizing properties of certain anionic and cationic detergents. 251 Mar 56

Endothelial cells play a critical role in thromboregulation by virtue of a surface-connected fibrinolytic system. Cultured endothelial cells synthesize and secrete tissue-type plasminogen activator (t-PA) which can bind to at least two discrete sites on the cell surface. These binding sites preserve the catalytic activity of t-PA and protect it from its physiological inhibitor (PAI-1). N-terminal glutamic acid plasminogen (Glu-PLG), the main circulating fibrinolytic zymogen, also interacts specifically with the endothelial cell surface. Binding is associated with a 12-fold increase in catalytic efficiency of plasmin generation by t-PA which may reflect conversion of Glu-PLG to its plasmin-modified form, N-terminal lysine plasminogen (Lys-PLG). Lipoprotein(a) is an atherogenic lipoprotein particle which contains the plasminogen-like apolipoprotein(a) bound to low density lipoprotein. We report here that lipoprotein(a) interferes with endothelial cell fibrinolysis by inhibiting plasminogen binding and hence plasmin generation. In addition, we demonstrate lipoprotein(a) accumulation in atherosclerotic lesions. These findings may provide a link between impaired cell surface fibrinolysis and progressive atherosclerosis.
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PMID:Lipoprotein(a) modulation of endothelial cell surface fibrinolysis and its potential role in atherosclerosis. 252 66

Positively charged molecules such as protamine, leukocyte cationic protein, and the carboxyl terminus of platelet factor 4 have been shown to increase fibrin fiber thickness. Synthetic homo poly(L-amino acids) were used to explore the role of charge and molecular weight of cationic molecules on fibrin assembly. The effects of poly(L-lysine) (PLL), poly(L-glutamic acid) (PLG), poly(L-aspartic acid) (PLA), poly(L-histidine) (PLH), and poly(L-arginine) (PLArg) on the assembly and structure of fibrin gels were studied by using light-scattering techniques. At a PLG (Mr 60,000) concentration of 80 micrograms/mL and a PLA (Mr 20,000) concentration of 64 microgram/mL, neither of these negatively charged polymers produced a detectable change in either fibrin assembly kinetics or final structure. Positively charged PLArg (16 micrograms/mL) caused a 30% increase in fibrin fiber mass/length ratio without calcium. In contrast, PLH (16 micrograms/mL), also positively charged, had no effect in the absence of CaCl2 but produced a 40% increase in fiber mass/length ratio with 5 mM CaCl2. At concentrations as low as 1 microgram/mL, positively charged PLL increased the initial fibrin assembly kinetics and led to larger fiber mass/length ratio. The impact on fibrin mass/length ratio was equivalent for three different molecular weight preparations of PLL (Mr 25,000, 90,000, and 240,000). The lack of a molecular weight effect on fiber thickness and the low polymer concentrations required to produce the perturbation argue against an excluded volume effect as the mechanism by which lateral fiber growth is augmented. Mechanisms by which poly(L-amino acids) may perturb fibrin assembly are discussed.
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PMID:Effect of homo poly(L-amino acids) on fibrin assembly: role of charge and molecular weight. 271 71

The effect of purified human activated protein C (APC) on fibrinolysis was studied using a clot lysis system consisting of purified glu-plasminogen, tissue-type plasminogen activator, plasminogen activator inhibitor (released from endothelial cells or blood platelets), fibrinogen, 125I-fibrinogen and thrombin. All proteins were of human origin. In this system APC could increase fibrinolysis in a dose dependent way, without affecting fibrin formation or fibrin crosslinking. However, this profibrinolytic effect of APC could only be observed when plasminogen activator inhibitor (PAI-1) was present. The effect of APC was completely quenched by pretreatment of APC with anti-protein C IgG or di-isopropyl-fluorophosphate. Addition of the cofactors of APC-protein S, Ca2+-ions and phospholipid-alone or in combination did not enhance the profibrinolytic effect of APC. These observations indicate that human APC can accelerate in vitro clot lysis by the inactivation of PAI-1 activity. However, the neutralization of PAI-1 by APC is independent of the presence or absence of protein S, phospholipid and Ca2+-ions.
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PMID:Activated protein C increases fibrin clot lysis by neutralization of plasminogen activator inhibitor--no evidence for a cofactor role of protein S. 297 9

Activation of the zymogen form of a serine protease is associated with a conformational change that follows proteolysis at a specific site. Tissue-type plasminogen activator (t-PA) is homologous to mammalian serine proteases and contains an apparent activation cleavage site at arginine-275. To clarify the functional consequences of cleavage at arginine-275 of t-PA, site-specific mutagenesis was performed to convert arginine-275 to a glutamic acid. The mutant enzyme (designated Arg-275----Glu t-PA) could be converted to the two-chain form by Staphylococcus aureus V8 protease but not by plasmin. The one-chain form was 8 times less active against the tripeptide substrate H-D-isoleucyl-L-prolyl-L-arginine-p-nitroanilide (S-2288), and the ability of the enzyme to activate plasminogen in the absence of fibrinogen was reduced 20-50 times compared to the two-chain form. In contrast, one-chain Arg-275----Glu t-PA has equal activity to the two-chain form when assayed in the presence of physiological levels of fibrinogen and plasminogen. Fibrin bound significantly more of the one-chain form of t-PA than the two-chain form for both the wild-type and mutated enzymes. One- and two-chain forms of the wild-type and mutated plasminogen activators slowly formed complexes with plasma protease inhibitors, although the one-chain forms showed decreased complex formation with alpha 2-macroglobulin. The one-chain form of t-PA therefore is fully functional under physiologic conditions and has an increased fibrin binding compared to the two-chain form.
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PMID:Functional role of proteolytic cleavage at arginine-275 of human tissue plasminogen activator as assessed by site-directed mutagenesis. 310 80

In the present study the activation of glu-plasminogen by fibrin-bound t-PA was determined by integrating spectrophotometric and computer analysis of the reaction. Our aim was to determine the parameters of the activation and to characterize the functional activity of t-PA. Our results indicate that the t-PA present in purified or crude sources such as plasma or culture supernatants, can be specifically identified using the methodology described in this report.
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PMID:Functional identification of t-PA in crude and purified systems. 314 63

An ideal thrombolytic (or fibrinolytic) agent is one which would generate the formation of plasmin only where it is required, i.e. bound to fibrin within the thrombus. However, the capacity of even the newer thrombolytic agents to achieve localised plasmin generation within the thrombus is relative and depends on the concentration of the agent administered. For all available activators, the concentration required for effective clinical thrombolysis is also capable of converting plasminogen to plasmin within the circulation (plasminaemia). Since the action of plasmin is not specific to fibrin, plasminaemia results in dissolution not only of fibrin but also of several other clotting factors. For example, plasmin can degrade fibrinogen and cause impaired haemostasis. The plasminogen activators which are available, or have been developed to date, include streptokinase, urokinase, pro-urokinase, anisoylated plasminogen-streptokinase activator complex (APSAC) and tissue plasminogen activator (t-PA). All of these agents have the same biochemical mechanism of action, cleaving an arginine-valine bond in the plasminogen molecule to form plasmin, but they differ with regard to other important properties. The first property to be considered is clot specificity; the ability to dissolve fibrin as opposed to fibrinogen, and also to dissolve the clot as opposed to a haemostatic plug. Unfortunately, fibrin specificity does not equate entirely with thrombus specificity, and all currently developed plasminogen activators, by dissolving fibrin, will induce the destruction of haemostatic extravascular plugs as well as intravascular thrombi. Thus, no agent is thrombus-specific in this respect. The degree of fibrinogenolysis does vary between plasminogen activators. Those which have the least effect on haemostasis or clotting capability would seem, at first, to be preferable. However, a short term reduction in fibrinogen could also be beneficial, since it may reduce the incidence of early reocclusion and, by reducing blood viscosity, improve microcirculation to the infarct zone. The intrinsic efficiency of the plasminogen activators is a second important property. In vitro, under conditions pertaining to the circulation, urokinase is about 10 times more efficient than t-PA at converting glu-plasminogen to plasmin (on the basis of the Vmax to Km ratio), while streptokinase-plasmin is 20 times more efficient. The efficiency of these activators is increased in the presence of fibrin and lys-plasminogen, 1800-fold for t-PA, 8-fold for urokinase and 180-fold for streptokinase-plasmin.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Preclinical pharmacological evaluation of anisoylated plasminogen streptokinase activator complex. 331 13

A bioimmunoassay (BIA) for tissue plasminogen activator (t-PA) is described which depends on the binding of t-PA and its inhibitor complexes to an immobilised IgG to t-PA and the subsequent assessment of the bound t-PA using glutamic acid-plasminogen (glu-plgn) and the chromogenic substrate, S-2251. This assay indicated that neither normal plasma nor its euglobulin precipitate contain any measurable free and functionally active t-PA. The BIA was also used to measure the level of the fast acting specific t-PA inhibitor (t-PA/INH) in plasma by assessing the residual t-PA activity in the plasma euglobulin fraction (pH 5.9), following the addition of a known amount of t-PA to the plasma.
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PMID:Bioimmunoassay (BIA) of tissue plasminogen activator (t-PA) and its specific inhibitor (t-PA/INH). 393 Dec 84


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