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:3.4.21.1 (chymotrypsin)
10,938 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Previous experiments demonstrated that chymotrypsin, but not adenosine diphosphate (ADP), exposed fibrinogen binding sites on platelets from patients with Glanzmann's thrombasthenia. Three of these patients have been reexamined, and previous observations were confirmed. The quantity of iodine 125-labeled glycoprotein IIb (GPIIb) and glycoprotein IIIa (GPIIIa) on the platelets of these patients was considerably less than normal but was detectable by immunoprecipitation, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and autoradiography. The amount of residual GPIIb and GPIIIa as measured by binding studies with radiolabeled monoclonal antibodies was between 3% and 12% of the normal value. Platelet suspensions from these patients did not aggregate with fibrinogen and did not bind 125I-fibrinogen on stimulation with ADP. However, incubation of these platelets with chymotrypsin or pronase resulted in fibrinogen binding and platelet aggregation. Monoclonal antibodies specific for the GPIIb-GPIIIa complex blocked both the fibrinogen binding and the aggregation of enzyme-treated platelets. The treatment of washed platelets of a fourth thrombasthenic patient with ADP or with chymotrypsin failed to result in fibrinogen binding and aggregation. However, the level of GPIIb and GPIIIa on these platelets as measured by a Western blot technique and by monoclonal antibody binding amounted to less than 0.35% to 0.5% of normal values. In conclusion, fibrinogen binding sites exposed on thrombasthenic platelets by chymotrypsin are derived from GPIIb-GPIIIa molecules. Aggregation of chymotrypsin-treated thrombasthenic platelets by fibrinogen appears to represent a sensitive test for detection of functionally active GPIIb-GPIIIa complex on the platelet surface.
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PMID:Aggregation of chymotrypsin-treated thrombasthenic platelets is mediated by fibrinogen binding to glycoproteins IIb and IIIa. 299 74

In situ proteolysis of Na,K-ATPase was studied using inside-out red cell membrane vesicles. Proteolysis of the enzyme in its "E1" conformation with either trypsin or chymotrypsin inactivated cation translocation more than ATP hydrolysis. This was evident both in the absence of intravesicular alkali cations when Na-ATPase was compared to ATP-dependent 22Na+ influx, and in the presence of K+ when Na+/K+ exchange was compared to (Na+ + K+)-activated ATPase. This differential loss in pump versus hydrolysis was observed also when the activities of only intact, non-leaky vesicles were compared and therefore reflects intramolecular uncoupling rather than nonspecific leakage. Although oligomycin and thimerosal, like trypsin and chymotrypsin, inhibit the enzyme's conformational step(s), neither effect uncoupling. It is concluded that specific cleavage(s) of Na,K-ATPase, at least as it exists in situ, alters the reaction sequence with respect to the normal ordered mechanism. Accordingly, cytoplasmic Na+ and extracellular K+ bind to the enzyme, stimulate phosphorylation (ATP + E1----E1P + ADP) and dephosphorylation (E2P----E2 + Pi), respectively, but each is then released to the same side from which it had bound; presumably release occurs prior to the conformational transitions of E1P to E2P and E2 to E1. This conclusion is supported by experiments showing that, ar micromolar ATP concentration, the hydrolytic activity (Na-ATPase) of the trypsinized but not the unmodified enzyme is stimulated by K+, consistent with earlier experiments (Hegyvary, C., and Post, R. L. (1971) J. Biol. Chem. 246, 5234-5240) showing that the K X E2 to K X E1 transition is slower than the E2 to E1 transition.
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PMID:Uncoupling the red cell sodium pump by proteolysis. 300 82

Stimulation of intact platelets by ADP results in a shape change followed by aggregation in the presence of fibrinogen. ADP was found to induce a shape change in chymotrypsin-treated platelets that was similar in extent and initial velocity to that of intact (untreated) platelets. Scanning-electron microscopy verified an ADP-induced shape change in chymotrypsin-treated platelets. This shape change could be completely blocked by stimulators of platelet adenylate cyclase (forskolin, prostaglandin E1, and prostacyclin). On the other hand, the aggregation of chymotrypsin-treated platelets by fibrinogen was not dependent on the presence of ADP and could not be blocked by forskolin, prostaglandin E1, or prostacyclin, even though the levels of cyclic AMP (cAMP) formed in chymotrypsin-treated platelets were comparable to levels that completely inhibited the ADP-induced aggregation of intact platelets. This lack of inhibition of platelet aggregation was not due to degradation of the adenylate cyclase or prostaglandin receptors, since chymotrypsin-treated platelets were found to have a functional adenylate cyclase system that could be stimulated by forskolin, prostaglandin E1, and prostacyclin and inhibited by ADP and epinephrine, similar to that of intact platelets. These results provide direct evidence that cAMP does not interact with fibrinogen binding sites once they have become permanently exposed on the surface of platelets. Pretreatment of platelets with chymotrypsin therefore appears to be a useful tool that allows for the dissociation of platelet shape change from aggregation, without inhibiting either response.
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PMID:Proteolysis of the platelet surface: dissociation of shape change from aggregation. 300 79

Inside-out membrane vesicles derived from human red cells were used to probe the effects of controlled tryptic digestion on the sodium pump as it exists in situ. Digestion of the enzyme in its E1 conformation resulted in several alterations which are generally similar to those reported for the purified kidney enzyme, namely (i) greater loss in overall hydrolytic activity compared to level of phosphoenzyme intermediate and (ii) cleavage of the alpha-subunit by trypsin as well as chymotrypsin at the cytoplasmic surface to yield a fragment of approx. 78 kDa. Tryptic digestion effected similar rates of inactivation of pump-mediated Na+-K+(Rb+) exchange, (ATP- plus ADP)-dependent Na+-Na+ exchange and, in the absence extracellular alkali cation, 'uncoupled' Na+ flux (Na+/0 flux). Alteration in the Na+:Rb+(K+) stoichiometry following trypsin cleavage could not be detected. The conformational transitions of phosphoenzyme and dephosphoenzyme are affected similarly by trypsin, as evidenced by similar inactivation rates of reactions through the 'forward' sequence involving the E1P to E2P transition as well as through the 'reserve' sequence involving the E1 to E2 transition.
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PMID:Tryptic modification of red-cell sodium pump behaviour. 300 33

Monobromobimane (mBBr, bimane), a compound that penetrates cells and forms a fluorescent adduct with thiol groups, was used to asses the significance of thiols in platelet function. Exposure of washed platelets for 1 min to 100 microM mBBr abolished ADP-induced aggregation; shape change was not inhibited by 500 microM mBBr. The nonpenetrating compound monobromotrimethylammoniobimane was ineffective. Established ADP-induced aggregation was reversed by bimane, and fibrinogen binding to ADP-stimulated platelets was inhibited, an effect mainly due to decreased number of binding sites. Aggregation stimulated by A23187 and arachidonate was less effectively inhibited whereas epinephrine- and collagen-induced aggregation were abolished by 50 microM mBBr. Similar effects on aggregation and secretion were observed in platelet-rich plasma except that higher mBBr concentrations were usually necessary. Aggregation and 14C-serotonin secretion stimulated by 0.1 U/ml thrombin were partially inhibited by pretreatment with bimane. With lower thrombin concentrations, they were often enhanced, as was 3H-arachidonate release. Bimane inhibited epinephrine-induced arachidonate release in gel-filtered platelets, possibly because it abolished the primary aggregation necessary for this release. mBBr did not elevate cyclic AMP but enhanced the increase induced by PGE1 and prevented the subsequent decrease typically caused by ADP. Examination of SDS polyacrylamide gels with ultraviolet light showed that mBBr reacted with many platelet proteins but not with GP IIb or IIIa. This observation, and the fact that bimane did not inhibit the fibrinogen-induced aggregation of DTT- or chymotrypsin-treated platelets suggest that it reacts with thiol group(s) that are involved in "exposing" the fibrinogen receptor.
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PMID:Modification of platelet functions by monobromobimane, a fluorescent thiol group label. 301 18

Tertiary amine local anesthetics modify a variety of platelet membrane-related functions. The present study explored dibucaine (DB)-induced inhibition of platelet cohesion by examining structural and functional alterations of the human platelet membrane glycoprotein IIb-IIIa complex (GPIIb-IIIa) and platelet Ca2+ homeostasis. Complete inhibition of ADP-induced aggregation was achieved five minutes after platelet exposure to 0.10 to 0.25 mmol/L of DB when fibrinogen binding was reduced by 50%. At higher concentrations of DB (approximately 1 mmol/L), ADP-induced fibrinogen binding was completely blocked. Scatchard analysis revealed loss of high-affinity binding sites in addition to reduction in Bmax. In contrast, chymotrypsin-treated platelets sustained 50% inhibition of fibrinogen binding when incubated with 0.4 to 0.5 mmol/L DB, and kinetic analysis showed that the high-affinity platelet-fibrinogen interactions were reduced but not absent. Fibrinogen binding to chymotrypsin-treated platelets could not be completely inhibited even at high DB concentrations (1 mmol/L). The inhibition of fibrinogen binding to chymotrypsin-treated platelets correlated with changes in binding of a monoclonal antibody (10E5) specific for an epitope on the GPIIb-IIIa complex. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and radioelectroimmunoassay of DB-treated platelets, however, showed no evidence of a reduction or degradation of GP IIb or IIIa. Platelet incubation with DB (five minutes, 0.1 to 1.0 mmol/L) was also accompanied by: increased platelet membrane-associated Ca2+ involving low-affinity binding sites [Kd = 5 X 10(-5) mol/L-]; increased 45Ca2+ uptake which correlated with degradation of actin-binding protein (ABP) and digestion of GPIb as visualized on periodic-acid Schiff (PAS)-stained SDS gels and as inferred from decreased binding of a monoclonal antibody (6D1) directed against this glycoprotein; and enhanced Ca2+ exchange. Thus, exposure of platelets to DB results in membrane-related alterations that may contribute to inhibition of platelet cohesion: Decreased fibrinogen receptor exposure by traditional agonists and diminished accessibility of the GPIIb-IIIa complex to extracellular ligands correlate with DB-induced inhibition of platelet aggregation; and increased calcium uptake and exchange across the platelet membrane likely leads to activation of the calcium-dependent protease(s) which was previously shown to correlate with DB-induced inhibition of ristocetin-induced platelet agglutination.
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PMID:Platelet membrane alterations induced by the local anesthetic dibucaine. 301 84

The accessibility of the tryptophans in dog kidney Na,K-ATPase was studied with the technique of quenching by acrylamide. By use of a modified Stern-Volmer equation, fa, the effective fraction of tryptophans most exposed to quencher, and Ka, the effective quenching constant, were calculated. The direct Stern-Volmer plots are nonlinear under nondenaturing conditions, indicating that the tryptophan residues are unequally accessible to quencher. Modified Stern-Volmer plots revealed marked differences in the exposure of tryptophans in the E1 and E2 states. In the presence of Na or ADP, ligands that stabilize E1, these plots curve downward, indicating that the in addition to buried (unquenched) tryptophans, there is a heterogeneous class of tryptophans. In the presence of K or ouabain, conditions that favor E2, the modified Stern-Volmer plots are linear, consistent with a homogeneous population of tryptophans. Treatment with chymotrypsin to block the E1 to E2 transition results in a new set of quenching parameters which are unchanged with Na or K. Even after detergent denaturation (1% sodium dodecyl sulfate for 30 min), Stern-Volmer plots are nonlinear, and a significant fraction of tryptophan residues remain inaccessible to quencher. Denaturation with urea or guanidine HCl plus dithiothreitol increases the fraction of quenchable fluorescence even more, but still a small fraction, about 7-13%, is buried. The observed changes in exposure of the tryptophan residues would seem to account for the differences in intrinsic fluorescence seen on adding K and Na to Na,K-ATPase. The present results provide new evidence that a significant rearrangement of amino acid residues results from the E1 to E2 transition. Furthermore, a region of the molecule is inaccessible even after denaturation; this may correspond to highly hydrophobic stretches that are normally buried in the membrane.
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PMID:Accessibility of tryptophan residues in Na,K-ATPase. 303 Oct 29

Calf thymus poly(ADP-ribose) synthetase (Mr = 120,000) is cleaved with papain into two fragments of M(r) = 74,000 and 46,000 and also split with chymotrypsin into two fragments of M(r) = 66,000 and 54,000. Each fragment purified to homogeneity is enzymatically inactive, but combined incubation of the 74,000 and 46,000 fragments in the presence of DNA restored 20% of the enzyme activity. In contrast, combined incubation of the 66,000 and 54,000 fragments does not restore any enzyme activity. In the former incubation, autopoly(ADP-ribosyl)ation reaction occurs exclusively on the 74,000 fragment. When each fragment is incubated with [adenine-U-14C]NAD in the presence of DNA and a catalytic amount of the native enzyme, poly(ADP-ribosyl)action occurs in the overlapped portion (22,000) of the 66,000 fragment and the 74,000 fragment. Nevertheless, the purified 22,000 fragment is a poor acceptor for poly(ADP-ribosyl)ation. The degree of poly(ADP-ribosyl)ation of the proteolytic fragments is significantly reduced by increasing NaCl concentration, probably due to the lack of the interaction between the enzyme fragments and DNA. These results, taken together, indicate that DNA is indispensable for the reconstitution of the catalytic activity as well as the poly(ADP-ribosyl)ation of the fragmented enzyme.
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PMID:Reconstitution and poly(ADP-ribosyl)ation of proteolytically fragmented poly(ADP-ribose) synthetase. 308 11

Butylidenephthalide inhibited, in a dose-dependent manner, the aggregation and release reaction of washed rabbit platelets induced by collagen and arachidonic acid. Butylidenephthalide also inhibited slightly the platelet aggregation induced by PAF and ADP, but not that by thrombin or ionophore A23187. Thromboxane B2 formation caused by collagen, arachidonic acid, thrombin and ionophore A23187 was in each case markedly inhibited by butylidenephthalide. Butylidenephthalide inhibited the aggregation of ADP-refractory platelets, thrombin-degranulated platelets, chymotrypsin-treated platelets and platelets in the presence of creatine phosphate/creatine phosphokinase. Its inhibition of collagen-induced aggregation was more marked at lower Ca2+ concentrations in the medium. The aggregability of platelets inhibited by butylidenephthalide could be recovered after the washing of platelets. In human platelet-rich plasma, butylidenephthalide and indomethacin prevented the secondary aggregation and blocked ATP release from platelets induced by epinephrine. Prostaglandin E2 formed by the incubation of guinea-pig lung homogenate with arachidonic acid could be inhibited by butylidenephthalide, indomethacin and aspirin. It is concluded that the antiplatelet effect of butylidenephthalide is mainly due to an inhibitory effect on cyclo-oxygenase and may be due partly to interference with calcium mobilization.
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PMID:Antiplatelet effect of butylidenephthalide. 310 95

The progressive stabilization of fibrinogen binding to ADP-treated platelets has been well described, but the nature of this interaction remains obscure. In the present study, irreversibly bound fibrinogen was defined as that fraction of bound iodinated fibrinogen that failed to dissociate from stimulated human gel-filtered platelets within 10 min of adding 10 mM ethylenediaminetetraacetic acid. It represented 16 +/- 11% (mean +/- SD, n = 10) of fibrinogen bound to ADP-treated platelets after 1 min and 52 +/- 11% of fibrinogen bound to these platelets after 60 min. Similar results were obtained if platelets were stimulated with purified human thrombin (0.1 U/ml) or epinephrine (10 microM). Irreversible fibrinogen binding was significantly reduced at 4 degrees C (27 +/- 9%, mean +/- SD, n = 6) if platelets were preincubated (30 min, 25 degrees C) with 30 micrograms/ml cytochalasin B or D (18 +/- 8%) or stimulated with chymotrypsin (0.5 mg/2-3 X 10(8) platelets) (31 +/- 8%). Formation of irreversible platelet-fibrinogen interactions correlated with the incorporation of actin and actin-binding protein into the Triton X-100-insoluble platelet cytoskeleton and the ability of platelets to retract fibrin clots. Irreversibly bound fibrinogen was available on platelets for digestion by 0.2 U/ml plasmin. The enzyme removed 96 +/- 6% (mean +/- SD, n = 6) of all bound fibrinogen from platelets after 30 min at 25 degrees C. This was not accompanied by significant release of [14C]serotonin or lactate dehydrogenase. Furthermore, platelets incubated with plasmin could bind fibrinogen normally after the enzyme had been neutralized with aprotinin.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Examination of irreversible platelet-fibrinogen interactions. 315 13


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