UNIPROT:P15088 - FACTA Search

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Query: UNIPROT:P15088 (mast cell)
14,925 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Pancreatic juices were collected by selective reverse catherism of the chief pancreatic duct in two patients, one free from pancreatic disease and the other having a pancreas cancer. They were analysed in detail especially in order to get information on the mechanism of enzyme excretion. The variations of the digestive enzyme activities (amylase, lipase, trypsin, chymotrypsin, carboxypeptidase A and B) were not superimposable among them or with the fluctuations of the protein concentration in the pancreatic juice samples. These results agree with a non-parallel enzyme-excretion mechanism by the pancreas. However deep electrophoresis analyses of pancreatic juice samples showed that the ratio of each digestive enzyme concentration remained almost constant in the same patient. This observation disagrees with the above conclusion and suggests that the data obtained by using classical methods for estimating digestive enzyme activities have to be considered prudently. By another way, two main significant differences were reported by analysing the ionic composition of the pancreatic juice samples following their origin. The pancreatic juice samples of the patient having a pancreas cancer had a lower and more variable Na+ concentration than those coming from the patient who was free from pancreas disease. They had a HCO3- concentration which was almost constant, contrary to what was observed for the pancreatic juice secreted by the other patient.
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PMID:[Detailed analysis of human pancreatic secretions collected by retrograde catheterization. Parallel or non-parallel excretion of digestive enzymes?]. 138 69

In RBL-2H3 rat basophilic leukemia cells, Ca2+ influx and secretion are activated by antigens that crosslink IgE-receptor complexes and by the Ca2+ ionophore, ionomycin. Here we report that antigen-stimulated Ca2+ influx and secretion are impaired and ionomycin-induced responses are strongly inhibited following the removal of HCO3- from the medium. These results raised the possibility that HCO3(-)-dependent pH regulation mechanisms play a role in the cascade of events leading to mast cell activation. To test this hypothesis, intracellular pH (pHi) was measured by ratio imaging microscopy in individual RBL-2H3 cells labeled with 2',7'-bis-(2-carboxyethyl)-5-(6) carboxyfluorescein (BCECF). In unstimulated cells, it was found that basal pHi in the presence of HCO3- is 7.26, significantly greater than pHi in its absence, 7.09 (P less than 10(-6]. These results, as well as evidence that pHi increases rapidly when HCO3- is added to cells initially incubated in HCO3(-)-free medium, indicate that unstimulated cells use a HCO3(-)-dependent mechanism to maintain cytoplasmic pH. Further analyses comparing unstimulated with stimulated cells showed that antigen causes a small transient acidification in medium containing HCO3- and a larger sustained acidification in HCO3(-)-depleted medium. Ionomycin is a more potent acidifying agent, stimulating a sustained acidification in complete medium and causing further acidification in HCO3(-)-free medium. These results support the hypothesis that the inhibition of antigen- and ionomycin-induced 45Ca2+ influx and secretion in cells incubated in HCO3(-)-free medium is at least partially due to the inactivation of HCO3(-)-dependent mechanisms required to maintain pH in unstimulated cells and to permit pH recovery from stimulus-induced acidification.
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PMID:Importance of bicarbonate ion for intracellular pH regulation in antigen- and ionomycin-stimulated RBL-2H3 mast cells. 154 61

The carbamate ester N-(phenoxycarbonyl)-L-phenylalanine binds well to carboxypeptidase A in the manner of peptide substrates. The ester exhibits linear competitive inhibition toward carboxypeptidase A catalyzed hydrolysis of the amide hippuryl-L-phenylalanine (Ki = 1.0 X 10(-3) M at pH 7.5) and linear noncompetitive inhibition toward hydrolysis of the specific ester substrate O-hippuryl-L-beta-phenyllactate (Ki = 1.4 X 10(-3) M at pH 7.5). Linear inhibition shows that only one molecule of inhibitor is bound per active site at pH 7.5. The hydrolysis of the carbamate ester is not affected by the presence of 10(-8)-10(-9) M enzyme (the concentrations employed in inhibition experiments), but at an enzyme concentration of 3 X 10(-6) M catalysis can be detected. The value of kcat at 30 degrees C, mu = 0.5 M, and pH 7.45 is 0.25 s-1, and Km is 1.5 X 10(-3) M. The near identity of Km and Ki shows that Km is a dissociation constant. Substrate inhibition can be detected at pH less than 7 but not at pH values above 7, which suggests that a conformational change is occurring near that pH. The analogous carbonate ester O-(phenoxycarbonyl)-L-beta-phenyllactic acid is also a substrate for the enzyme. The Km is pH independent from pH 6.5 to 9 and has the value of 7.6 X 10(-5) M in that pH region. The rate constant kcat is pH independent from pH 8 to 10 at 30 degrees C (mu = 0.5 M) with a limiting value of 1.60 s-1. Modification of the carboxyl group of glutamic acid-270 to the methoxyamide strongly inhibits the hydrolysis of O-(phenoxycarbonyl)-L-beta-phenyllactic acid. Binding of beta-phenyllactate esters and phenylalanine amides must occur in different subsites, but the ratios of kcat and kcat/Km for the structural change from hippuryl to phenoxy in each series are closely similar, which suggests that the rate-determining steps are mechanistically similar.
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PMID:Interaction of carboxypeptidase A with carbamate and carbonate esters. 362 Apr 47

N-(4-Methoxyphenylazoformyl)-L-phenylalanine is efficiently cleaved by the enzyme bovine carboxypeptidase A into fragments anisole, molecular nitrogen, carbonate, and phenylalanine, in the course of which an intense spectral absorption of the substrate (epsilon350 = 19,000 M-1 cm-1) disappears completely. This furnishes a sensitive spectrophotometric detection of the protease. Steady-state catalytic velocity depends upon enzyme and substrate concentrations in the normal manner, and a Michaelis-Menten Km value of 0.11 mM and a kcat value of 44 s-1 were measured at pH 7.5 in saline solution. These parameters have a pH dependence typical for the enzyme. With saturating amounts of substrate, a solution containing 10 nM enzyme produces a spectral absorptivity change at 350 nm of -0.03 a.u./min (1-mm pathlength), suitable for assay purposes. Catalysis may alternatively be monitored at wavelengths as long as 400 nm.
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PMID:Arazoformyl peptide surrogates as spectrophotometric kinetic assay substrates for carboxypeptidase A. 881 13

In rat mast cells Ca(2+) entry is modified by the presence or absence of other ions in the external medium. HCO3(-) ions, which modify mast cell degranulation, seemed to modulate the Ca(2+) entry elicited by the intracellular Ca(2+)-ATPase inhibitor thapsigargin. In this work we studied the regulation of the Ca(2+) entry by HCO3(-) and its relationship with exocytosis. The Ca(2+) entry was activated by thapsigargin and Ca(2+) in mast cells bathed by a HCO3(-)-buffered medium or a HCO3(-)-free medium. Both Ca(2+) entry and exocytosis were enhanced by the presence of HCO3(-) ions. Nondegranulated mast cells showed a low Ca(2+) entry either in the presence or absence of HCO3(-). Thus, mast cells with a high [Ca(2+)](i) increase in a HCO3(-)-buffered medium undergo degranulation. In the same cells a second Ca(2+) entry was significantly higher than the first Ca(2+) entry in a HCO3(-)-free medium, while in a HCO3(-)-buffered medium the first and second Ca(2+) entries reached similar [Ca(2+)](i) levels. Although the second Ca(2+) entry is high in a HCO3(-)-free medium, degranulation is still low. Our results demonstrate that HCO3(-) ions increase the capacitative Ca(2+) entry and the sensitivity of mast cells to intracellular Ca(2+) in order to induce degranulation.
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PMID:HCO3(-) ions increase mast cell sensitivity to thapsigargin-induced Ca(2+) entry. 1116 48

We examined the effect of NO on acid secretion in vitro using isolated preparations of Bullfrog stomach. The bullfrog fundic mucosa was bathed in unbuffered Ringer solution gassed with 100% O2 on the mucosal side and HCO3- Ringer's solution gassed with 95% O2/5% CO2 on the serosal side, and the acid secretion was measured at pH 5.0 using the pH-stat method and by adding 5 mM NaOH. Serosal addition of a NO donor NOR-3 (10(-5) approximately 10(-3) M: (+/-)-(E)-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexnamine) caused an increase of acid secretion in a dose-dependent manner, the effect lasting about 1 hr and reaching a maximal level of 2-fold the basal values. The acid stimulatory effect of NOR-3 was mimicked by another NO donor SNAP (10(-3) mol/L: S-nitroso-O-N-acetyl-penicillamine) and markedly and markedly inhibited by prior administration of cimetidine (10(-5) mol/L) as well as compound 48/80 (the mast cell degranulator). Likewise, the increased acid response to NOR-3 was significantly mitigatd by pretreatment with carboxy-PTIO (a NO scavenger) or superoxide dismutase (SOD), but not by indomethacin or methylene blue (a guanylyl cyclase inhibitor). Neoither L-NAME, L-arginine nor dibutyryl guanosine-3',5'-cyclic monophosphate (dbcGMP) has any effect on the basal acid secretion. Serosal addition of NOR-3 caused a significant increase in the luminal release of histamine, and this response was inhibited by pretreatment with either compound 48/80, carboxy-PTIO or SOD. These results suggest that the NO donor increases gastric acid secretion in the isolated frog stomach in vitro, and this action is mediated by endogenous histamine released from mast cells, the process being cGMP-independent but requiring the presence of superoxide radicals. In addition, it was speculated that the histamine releasing action of NO may be due to peroxynitrite produced by NO and superoxide radicals.
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PMID:Stimulation by nitric oxide of gastric acid secretion in bullfrog fundic mucosa in vitro. 1132 16

A model for the natural enzyme carboxypeptidase A was prepared by molecular imprinting in synthetic polymers. An unusually high activity and efficiency for carbonate hydrolysis could be obtained by imprinting with a stable transition-state analogue template and introducing an amidinium group and a Cu2+ ion-binding site in a defined orientation to each other into the active site. With substrates having a very similar structure to the template, extraordinarily high enhancements of rates of 110 000-fold were obtained of catalyzed to uncatalyzed reaction kcat/kuncat . The efficiency kcat/Km of the molecularly imprinted catalysts compared to that of the nonimprinted control polymers containing the same functional groups was 790-fold higher, a clear indication of a very efficient imprinting procedure.
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PMID:Functional mimicry of the active site of carboxypeptidase a by a molecular imprinting strategy: cooperativity of an amidinium and a copper ion in a transition-state imprinted cavity giving rise to high catalytic activity. 1519 87

The human mast cell line (HMC-1) has been used to study the relationship between intracellular pH and cytosolic calcium (Ca2+) in mast cells. Thapsigargin (TG) caused store-operated Ca2+ entry, that is enhanced by the PKC activator PMA. NH4Cl-induced alkalinization showed an inhibitory effect on TG-sensitive stores depletion (not on TG-insensitive stores), and also on final cytosolic Ca2+ levels reached in response to both TG and the ionophore ionomycin. Loperamide, a positive modulator of store-operated channels, induced a slight Ca2+ entry by itself, and also increased TG-induced Ca2+ entry. This enhancement was not enough to reverse the inhibitory effect of NH4Cl-induced alkalinization. When comparing the effect of NH4Cl-induced alkalinization on Ca2+ levels, with those observed using Ca2+ channel blockers (namely Ni2+ and SKF-96365), cytosolic profiles for this ion are different, either in modified saline solution or in HCO3(-)-free medium. Thus, it seems unlikely that the inhibitory effect of NH4Cl-induced alkalinization on Ca2+ is taking place by blockage of Ca2+ entry. Furthermore, inhibition of the plasma membrane Ca2+-ATPase (an important mechanism for Ca2+ efflux) with sodium orthovanadate (SO) matches with the inhibition of the negative effect on Ca2+ levels elicited by NH4Cl. Data indicate that NH4Cl-induced alkalinization might be activating Ca2+ efflux from the cell, by stimulation of the plasma membrane Ca2+-ATPase, and also confirm our previous finding that Ca2+ is a secondary signal to activate HMC-1 cells.
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PMID:Calcium-pH crosstalks in the human mast cell line HMC-1: intracellular alkalinization activates calcium extrusion through the plasma membrane Ca2+-ATPase. 1681 37

An artificial model for the natural enzyme carboxypeptidase A has been constructed by molecular imprinting in synthetic polymers. The tetrahedral transition state analogues (TSAs 4 and 5) for the carbonate hydrolysis have been designed as templates to allow incorporation of the main catalytic elements, an amidinium group and a Zn(2+) or Cu(2+) center, in a defined orientation in the transition state imprinted active site. The complexation of the functional monomer and the template in presence of Cu(2+) through stoichiometric noncovalent interaction was established on the basis of (1)H NMR studies and potentiometric titration. The Cu(2+) center was introduced into the imprinted cavity during polymerization or by substitution of Zn(2+) in Zn(2+) imprinted polymers. The direct introduction displayed obvious advantages in promoting catalytic efficiency. With substrates exhibiting a very similar structure to the template, an extraordinarily high enhancement of the rate of catalyzed to uncatalyzed reaction (k(cat)/k(uncat)) of 10(5)-fold was observed. If two amidinium moieties are introduced in proximity to one Cu(2+) center in the imprinted cavity by complexation of the functional monomer 3 with the template 5, the imprinted catalysts exhibited even higher activities and efficiencies for the carbonate hydrolysis with k(cat)/k(uncat) as high as 410,000. These are by far the highest values obtained for molecularly imprinted catalysts, and they are also considerably higher compared to catalytic antibodies. Our kinetic studies and competitive inhibition experiments with the TSA template showed a clear indication of a very efficient imprinting procedure. In addition, this demonstrates the important role of the transition state stabilization during the catalysis of this reaction.
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PMID:Functional mimicry of carboxypeptidase A by a combination of transition state stabilization and a defined orientation of catalytic moieties in molecularly imprinted polymers. 1851 Mar 22

The impressive efficiency and selectivity of biological catalysts has engendered a long-standing effort to understand the details of enzyme action. It is widely accepted that enzymes accelerate reactions through their steric and electronic complementarity to the reactants in the rate-determining transition states. Thus, tight binding to the transition state of a reactant (rather than to the corresponding substrate) lowers the activation energy of the reaction, providing strong catalytic activity. Debates concerning the fundamentals of enzyme catalysis continue, however, and non-natural enzyme mimics offer important additional insight in this area. Molecular structures that mimic enzymes through the design of a predetermined binding site that stabilizes the transition state of a desired reaction are invaluable in this regard. Catalytic antibodies, which can be quite active when raised against stable transition state analogues of the corresponding reaction, represent particularly successful examples. Recently, synthetic chemistry has begun to match nature's ability to produce antibody-like binding sites with high affinities for the transition state. Thus, synthetic, molecularly imprinted polymers have been engineered to provide enzyme-like specificity and activity, and they now represent a powerful tool for creating highly efficient catalysts. In this Account, we review recent efforts to develop enzyme models through the concept of transition state stabilization. In particular, models for carboxypeptidase A were prepared through the molecular imprinting of synthetic polymers. On the basis of successful experiments with phosphonic esters as templates to arrange amidinium groups in the active site, the method was further improved by combining the concept of transition state stabilization with the introduction of special catalytic moieties, such as metal ions in a defined orientation in the active site. In this way, the imprinted polymers were able to provide both an electrostatic stabilization for the transition state through the amidinium group as well as a synergism of transition state recognition and metal ion catalysis. The result was an excellent catalyst for carbonate hydrolysis. These enzyme mimics represent the most active catalysts ever prepared through the molecular imprinting strategy. Their catalytic activity, catalytic efficiency, and catalytic proficiency clearly surpass those of the corresponding catalytic antibodies. The active structures in natural enzymes evolve within soluble proteins, typically by the refining of the folding of one polypeptide chain. To incorporate these characteristics into synthetic polymers, we used the concept of transition state stabilization to develop soluble, nanosized carboxypeptidase A models using a new polymerization method we term the "post-dilution polymerization method". With this methodology, we were able to prepare soluble, highly cross-linked, single-molecule nanoparticles. These particles have controlled molecular weights (39 kDa, for example) and, on average, one catalytically active site per particle. Our strategies have made it possible to obtain efficient new enzyme models and further advance the structural and functional analogy with natural enzymes. Moreover, this bioinspired design based on molecular imprinting in synthetic polymers offers further support for the concept of transition state stabilization in catalysis.
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PMID:Design of biomimetic catalysts by molecular imprinting in synthetic polymers: the role of transition state stabilization. 2196 89

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