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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Thrombin stimulates polyphosphoinositide hydrolysis in embryonic chick heart cells and in 1321N1 astrocytoma cells and increases intracellular Ca2+ in the 1321N1 cells. The serine protease trypsin mimics these actions in a dose-dependent fashion, whereas the proteolytically inactive thrombin derivatives diisopropyl fluorophosphate-thrombin (DIP-thrombin) and D-phenylalanyl-L-prolyl-L-arginine chloromethyl ketone-thrombin (PPACK-thrombin) are ineffective in this regard. The phosphoinositide responses to thrombin or trypsin and the muscarinic agonist carbachol are additive, but no additivity is observed between the responses to thrombin and trypsin. Unlike the response to carbachol, the phosphoinositide and Ca2+ responses to thrombin and trypsin desensitize, with no recovery of the calcium response even when Ca2+ stores are replenished. Cross-desensitization of phospholipase C activation and calcium mobilization between these proteases is also observed. In addition, PPACK-thrombin, which elicits no response itself, effectively inhibits trypsin-stimulated phosphoinositide hydrolysis. It is proposed that thrombin and trypsin act through the same receptor. Proteolysis appears to be important in the mechanism by which these agonists elicit phosphoinositide hydrolysis, calcium mobilization, and, perhaps, subsequent receptor desensitization.
Mol Pharmacol 1989 Jul
PMID:Thrombin and trypsin act at the same site to stimulate phosphoinositide hydrolysis and calcium mobilization. 254 47

The first part of the present review is focused on structural aspects concerning the so far studied casein fractions of various origins: they are compared to the four classical major bovine caseins (alpha s1-, alpha s2-, beta- and kappa). The calcium-sensitive casein fractions are always phosphorylated whereas kappa-caseins are glycosylated. The study of the casein genes showed that the calcium-sensitive caseins diverged from a common ancestral gene and during the evolution, intergenic and intragenic duplications occurred. The considerable conservation of the phosphorylation sites emphasizes the importance of phosphorylated residues for the function of caseins, i.e. the formation of micelles and the binding of Ca2+. In kappa-caseins all the prosthetic sugar groups are linked by O-glycosidic linkages: their number varies from 0 to 5 in bovine kappa-casein and up to 10 in human kappa-casein. The structures of the known kappa-casein carbohydrate moieties are described. Finally the milk clotting process (interaction kappa-casein/chymosin) is compared to the blood clotting process (interaction fibrinogen/thrombin): a large number of similarities could be noted between both clotting phenomena. The second part of the review is devoted to the study of short casein peptides endowed with various biological activities. Some of them behaved as immunomodulators or casomorphins or angiotensin I converting enzyme inhibitors; others demonstrated an effect on platelet functions. A 'strategic zone' containing immunostimulating and opioid peptides could be located in cow and human beta-caseins. Furthermore bitter peptides, emulsifying peptides, calcium absorption enhancing peptides, chymosin-inhibiting peptides, have also been described and several further properties have been attributed to the kappa-caseinoglycopeptide; two tetrasaccharides isolated from the latter possess blood group activities. In conclusion caseins, the main milk proteins, should not only be considered as a nutriment but as a possible source of biologically active components. If, in the future, some of the discussed active peptides cannot be characterized in vivo, they can all, nevertheless, be synthesized and used either as food additives or in pharmacology.
Mol Cell Biochem 1989 May 04
PMID:Caseins of various origins and biologically active casein peptides and oligosaccharides: structural and physiological aspects. 267 66

Human alpha-thrombin, inhibited with the high-affinity irreversible inhibitor D-Phe-Pro-Arg-chloromethylketone, has been crystallized from polyethylene glycol 8000 solutions buffered with 0.1 M-sodium phosphate. The crystals are: orthorhombic, a = 67.9(1) A, b = 87.9(1) A, c = 61.0(1) A, space group P2(1)2(1)2(1) with four molecules per unit cell. This gives a protein fraction of 58% consistent with the excellent X-ray diffraction quality of the crystals. A mercury heavy-atom derivative is being prepared from a thioester analogue of D-Phe-Pro-Arg-CH2-alpha-thrombin in anticipation of a complete crystallographic structure determination.
J Mol Biol 1989 Apr 20
PMID:Human D-Phe-Pro-Arg-CH2-alpha-thrombin crystallization and diffraction data. 273 17

Platelet-activating factor (PAF) receptor-coupled activation of phosphoinositide-specific phospholipase C (PLC) was studied in platelets that were made refractory, by short-term pretreatments, to either PAF or thrombin. Generation of [3H]inositol triphosphate ( [3H]IP3) was monitored specifically for this purpose. [3H]Inositol-labeled rabbit platelets that were incubated (10 min) with increasing concentrations of PAF and subsequently challenged by the same concentration of PAF had greatly diminished PLC activity ( [3H]IP3 production) as compared to controls. Platelets incubated (10 min) with fixed concentrations of PAF and then challenged with increasing concentrations of PAF had log-dose response curves of [3H]IP3 production progressively shifted to the right (i.e., to higher concentrations) and were depressed as the PAF pretreatment with 10 nM PAF became completely refractory to further PAF stimulation of PLC. Washing the pretreated platelets with either buffer or buffer containing 0.5% bovine serum albumin did not restore the PAF for 10 min), platelets remained fully responsive to thrombin (2 units/ml)-stimulated production of [3H]IP3. Platelets pretreated with increasing concentrations of thrombin (0.15-2 units/ml) for different times (5-40 min) became refractory to both thrombin and PAF. It is concluded that PAF receptor-coupled activation of PLC becomes refractory (desensitized) in platelets preexposed to PAF, whereas platelets pretreated with thrombin are desensitized to both thrombin and PAF. It is proposed that thrombin has two transmembrane pathways leading to the activation of PLC, one shared with PAF and another utilizing separate mechanistic inputs.
Mol Pharmacol 1988 Jan
PMID:Desensitization of receptor-coupled activation of phosphoinositide-specific phospholipase C in platelets: evidence for distinct mechanisms for platelet-activating factor and thrombin. 282

Components of the CDw18 leukocyte surface glycoprotein complex (Mo1/LFA-1/GP 150,95 or MAC-1, LFA-1 family) are required for some adhesion-related functions of human neutrophils (PMNs). We evaluated the ability of monoclonal antibodies (MoAb) directed against specific determinants on the CDw18 glycoproteins to inhibit neutrophil adherence to cultured human endothelial cells (EC) stimulated by a variety of agonists, including thrombin and leukotriene C4, which induce the EC-dependent adhesion of PMNs. MoAb 60.3, an antibody that binds to an epitope common to the 3 heterodimer subunits of the neutrophil CDw18 complex, potently inhibited (90-100%) the rapid (5-30 minute) adherence response stimulated by N-formyl-methyionyl-leucyl-phenylalanine, leukotriene B4, platelet-activating factor, phorbol myristate acetate, Ionophore A23187, and tumor necrosis factor. MoAbs directed against epitopes on the alpha polypeptide of the CD11b (Mol, MAC-1) heterodimer also inhibited PMN adherence to EC and to cell-free surfaces induced by these agonists. In contrast, the anti-CDw18 MoAbs had a trivial effect on maximal EC-dependent neutrophil adherence stimulated by thrombin and leukotriene C4, and incompletely inhibited PMN adherence induced by these agonists under submaximal conditions. These findings indicate that there is an alternative mechanism for neutrophil adherence, presumably resulting from molecular alterations of the EC surface, that does not require the PMN CDw18 glycoproteins. They also suggest that the inability to adhere to endothelium may not completely account for the defect in chemotaxis that is observed in vivo in neutrophils that are deficient in the CDw18 complex.
 ...
PMID:Neutrophil adherence to human endothelium in vitro occurs by CDw18 (Mo1, MAC-1/LFA-1/GP 150,95) glycoprotein-dependent and -independent mechanisms. 282 29

Carbon monoxide (CO) inhibits human platelet aggregation triggered with threshold levels of agonists like arachidonate, ADP, collagen, thrombin, or the prostaglandin endoperoxide analogue U46619. This inhibition is counteracted by illumination with light above 400 nm indicating the involvement of a ferrous hemoprotein. An earlier suggestion that the mechanism of CO inhibition involves the cytochrome P450 protein thromboxane A2 synthase was ruled out as well as the involvement of the iron containing enzymes like cyclooxygenase or 12-lipoxygenase. In the presence of CO, no arachidonate was released from phospholipids, no increase of intracellular calcium levels was observed, and phospholipase C was not activated suggesting that the transducing mechanisms from the receptors to phospholipase C was effected in the presence of CO. cAMP levels were also unchanged but cGMP levels showed an increase of about 30%. By comparison with the guanylate cyclase stimulator nitroprusside, it was shown that such levels could block aggregation. In a 10,000 X g supernatant, CO enhanced guanylate cyclase activity 4-fold, supporting the view that CO acts by increasing platelet cGMP levels. With respect to the mechanism of guanylate cyclase action, the binding of CO to the regulatory subunit of guanylate cyclase must be responsible for the observed activation. It is concluded that cGMP is an important feedback regulator of the Pl response and that already a 25% increase in its steady state levels can cause inhibition of platelet aggregation.
Mol Pharmacol 1987 Oct
PMID:Inhibition of platelet aggregation by carbon monoxide is mediated by activation of guanylate cyclase. 289 93

The metabolism of atriopeptin prohormone ANF1-126 was examined with the aid of two separate radioimmunoassays, one detecting the C-terminal atriopeptins and the other detecting a fragment of the prohormone N-terminus. Intact prohormone standards are recognized in both assays, whereas the C-terminal atriopeptins are only detected by the atriopeptin assay. Both atriopeptin and N-terminal fragment immunoreactivities were detected in rat plasma and were simultaneously elevated following intravenous administration of desamino-arginine-vasopressin. Atriopeptin immunoreactivity returned to basal levels within 60 min after desamino-arginine vasopressin administration, whereas the N-terminal fragment immunoreactivity remained elevated for more than 2 hr. Analysis of both acid-boiled and sodium dodecyl sulfate-boiled rat atrial extracts by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting revealed the presence of a single high molecular weight species which reacted to both antisera and which comigrated with atriopeptin prohormone standards. Western blots of plasma from desamino-arginine vasopressin-stimulated rats yielded both the low molecular weight C-terminal atriopeptin and a high molecular weight N-terminal fragment-reactive peak which was smaller than the prohormone standards and which did not possess atriopeptin immunoreactivity. A recombinant 128-amino acid atriopeptin prohormone construct, ANF1-126-Arg-Arg, was used as a model substrate for prohormone metabolism. ANF1-126-Arg-Arg was specifically cleaved followed incubation with thrombin to yield the 98-amino acid N-terminal fragment and the C-terminal atriopeptin, AP28-Arg-Arg. Processing of ANF1-126-Arg-Arg by reperfusion through an isolated heart or by incubation in serum yielded identical metabolites to those generated by incubation with thrombin. No significant metabolism was observed following incubation of the prohormone with rat plasma. We conclude that the rat heart contains the necessary enzyme to cleave both endogenous and exogenous prohormone to atriopeptin and that processing by blood enzymes is not required.
Mol Pharmacol 1986 Dec
PMID:Proteolytic processing of atriopeptin prohormone. 294 28

The diterpene, forskolin, increases basal adenylate cyclase activity in membranes of human platelets to more than 20-fold with an EC50 of about 5 microM. However, when the platelet adenylate cyclase was activated via the stimulatory coupling component, Ns, e.g., by the hormone, prostaglandin E1, or the stable GTP analog, guanosine 5'-[gamma-thio]triphosphate, added in combination with a protease, forskolin was able to inhibit the enzyme. The inhibition was half-maximal and maximal (40-50% inhibition) at 0.01 and 0.1 microM forskolin, respectively, and occurred without apparent lag phase. At a maximally inhibitory concentration, forskolin largely reduced the apparent affinity of the Ns-stimulated platelet adenylate cyclase for its substrate MgATP in a noncompetitive manner, which resulted in a pronounced inhibition by forskolin at low substrate concentrations and a further increase in activity at high MgATP concentrations. Treatment of intact platelets or platelet membranes with agents known to interfere with Ni-mediated adenylate cyclase inhibition did not diminish but even increased the forskolin-induced inhibition of the adenylate cyclase. However, inhibition of the prostaglandin E1-stimulated adenylate cyclase by forskolin and the inhibitory hormonal agents, thrombin and epinephrine, were not additive at maximally inhibitory concentrations. Furthermore, increasing concentrations of Mg2+ and Mn2+ reduced (Mg2+) or even reversed (Mn2+) the forskolin-induced inhibition. The data indicate that forskolin apparently has two distinct effects on the platelet adenylate cyclase, namely inhibition and stimulation. The data furthermore suggest that the adenylate cyclase inhibition by forskolin is not mediated by the inhibitory guanine nucleotide-binding protein Ni, but may be due to an action of the diterpene at the adenylate cyclase catalytic moiety, particularly when activated by Ns, or a closely related membrane component.
Mol Pharmacol 1986 Mar
PMID:Inhibition of Ns-stimulated human platelet adenylate cyclase by forskolin. 300 33

The clearance of thrombin seems to occur at more than one site and by different mechanisms. This contributes to maintaining thrombin at the right concentrations to act optimally on its various substrates, and thus, to produce the proper amount of proteolytic conversions so that coagulation is precisely controlled. The vascular endothelium plays a major role in thrombin regulation and clearance. It contains heparin-like binding sites and thrombomodulin which serve as cofactors for the thrombin-antithrombin III reaction and the activation of protein C, respectively. In addition, thrombomodulin also serves as a receptor for endothelial cell mediated thrombin endocytosis. Thrombin clearance, which occurs following reaction with antithrombin III or thrombomodulin, probably takes place at different stages in hemostasis.
Mol Cell Biochem 1986 Aug
PMID:Clearance of thrombin in vivo: significance of alternative pathways. 302 20

Fluid phase heparin inhibits formation of the classical and alternative pathway C3 convertase of complement in assays performed either with purified complement proteins or in whole serum. Experiments using oligosaccharides of homogeneous mol. wt obtained by mild nitrous hydrolysis of heparin, demonstrated that the inhibitory activity of heparin increased exponentially with mol. wt for fragments containing between 4 and 14 saccharidic units and that fragments of mol. wt above 4700 (greater than 14 saccharidic units) had a similar anti-complementary activity to that of native heparin. Fragments of homogeneous mol. wt (octasaccharides) separated by ion exchange chromatography on the basis of negative charges, exhibited increasing inhibitory activity with increasing sulfate content. Over-sulfation of fragments of defined mol. wt resulted in a constant enhancement of the relative capacity of each fragment species to inhibit formation of the classical and alternative pathway C3 convertases. A synthetic pentasaccharide representing the minimal critical sequence responsible for the binding of heparin to anti-thrombin III exhibited a similar inhibitory capacity on formation of the C3 convertases as another synthetic pentasaccharide that was devoid of anti-Xa activity. These studies contribute to define a minimal structure of the heparin molecule with C3b- and C4b-binding capacity and definitively establish the independency of the anti-coagulant and anti-complementary sites on the heparin molecule.
Mol Immunol 1988 Sep
PMID:Structure-function relationships in the inhibitory effect of heparin on complement activation: independency of the anti-coagulant and anti-complementary sites on the heparin molecule. 321 Nov 61


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