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Query: UNIPROT:P06889 (Mol)
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Isolated sheep cardiac Purkinje fibers were pulled through a latex membrane and both segments were independently superfused with modified Tyrode solutions. Transmembrane potentials and intracellular pH (pHi) were continuously measured in one segment (test compartment, TC), using double-barreled pH sensitive glass microelectrodes, while the internal H+ activity was altered in the adjacent part of the fiber (experimental compartment, EC). In the latter local pHi changes were produced by removal of CO2/HCO3-, by superfusing acidic (pH 6.8) solution, and by addition and subsequent withdrawal of NH4Cl. Withdrawal of CO2/HCO3- in EC was found to have no influence on pHi in TC at 0.35 to 1.0 mm distance. The action potential first shortened and later on prolonged above control duration after switching to HCO3- -free medium. Perfusing EC with an acidic solution had virtually no effect on pHi in TC while action potential duration (APD) increased. Addition and withdrawal of NH4+ in EC decreased, respectively increased, APD. In TC no change in pHi was observed at 0.8 to 1.0 mm distance. At shorter distance a slow acidification was seen, associated with the presence of NH4+ in EC. The presence of amiloride, a blocker of the pHi regulating mechanism, could not unmask a larger pHi change. It is concluded that, in cardiac muscle, large gradients of pHi are possible over a relatively short distance, while electrotonic interaction can produce changes in the time course of the action potential in neighbouring cells having a normal intracellular pH.
J Mol Cell Cardiol 1988 Mar
PMID:Influence of local intracellular pH changes on pH and action potentials in adjacent parts of cardiac Purkinje fibers. 313 14

The chicken erythrocyte anion transport protein (band 3 of the erythrocyte cytoskeleton) is a central component taking part in two widely divergent functions of erythroid cells; it is a primary determinant of cytoskeletal architecture and responsible for electroneutral Cl-/HCO3- exchange across the plasma membrane. To analyze interesting aspects of the developmental regulation of this gene, we have cloned the cDNA and genomic counterparts of the erythroid-specific anion transport protein. We show that a single genetic locus for band 3 encodes two different erythroid cell-specific mRNAs, with different translational initiation sites, which predict polypeptides of sizes very close to those observed in vivo. In vitro translation and immune precipitation of synthetic mRNA derived from one putative fully encoding cDNA clone demonstrate that this clone gives rise to a protein which is identical in size and antigenicity to bona fide chicken erythroid band 3.
Mol Cell Biol 1988 Oct
PMID:Two different mRNAs are transcribed from a single genomic locus encoding the chicken erythrocyte anion transport proteins (band 3). 318 55

Glycosomal membranes of bloodstream form Trypanosoma brucei were purified to apparent homogeneity by sodium carbonate treatment and found to contain two major integral membrane proteins of 26 kDa (band 10) and 24 kDa (band 11). The procyclic-form glycosomal membranes isolated by the same procedure also resulted in a homogeneous preparation, but each piece of membrane thus purified was associated with an electron-dense granule. Procyclic membranes also contained primarily bands 10 and 11. These two proteins were selectively reduced by protease treatment of intact glycosomes, suggesting surface exposed domain(s) of the two proteins accessible to proteolytic digestion. They and band 8 protein also vanished in glycosomal lysates by apparent proteolysis, implying the presence of a specific protease which degrades the integral membrane proteins upon the loss of membrane integrity. The two proteins, hydrophobic in nature and apparently unglycosylated, have no known biological functions, but their possible involvement in translocating precursor proteins from the cytoplasm into the glycosome of T. brucei is postulated.
Mol Biochem Parasitol 1987 Aug
PMID:Identification of two integral glycosomal membrane proteins in Trypanosoma brucei. 367 Mar 44

The effect of high K+/low Na+-Tyrode's solution on Ca2+ uptake into neonatal rat atrium was studied using 45Ca2+. Substitution of 60-129 mM Na+ in Tyrode's solution by equimolar concentrations of K+ or choline, significantly (with the exception of 60 mM choline substitution) increased Ca2+ uptake above control. Furthermore, the Ca2+ uptake stimulated by K+ substitution was significantly greater than that stimulated by choline substitution at the corresponding concentrations. The choline/low Na+-induced Ca2+ uptake (i.e. that above the Ca2+ uptake measured in normal Tyrode's solution) was increased by pre-exposure to either ice-cold Tyrode's solution for 1 h (approximately 36% increase) or to K+-free Tyrode's solution for 3 h (approximately 100% increase). The choline/low Na+-induced Ca2+ uptake was abolished by the hypertonic addition of NaCl (returning the bathing Na+ concentration to normal), increased (approximately 140%) by the addition of 1.8 mM PO4(3-)-free Hepes buffered choline/low Na+ media, but unaffected by 0.2 mM cadmium. The high K+/low Na+-induced Ca2+ uptake (i.e. that above the Ca2+ uptake measured in normal Tyrode's solution) was relatively insensitive to pre-exposure to cold (0% change) or K+-free media (11% increase) and only 50% inhibited by the hypertonic addition of NaCl (returning the bathing Na+ concentration to normal). However, the high K+/low Na+-induced Ca2+ uptake was 57% inhibited by 0.2 mM cadmium and approximately 30% inhibited by the addition of 1.8 mM PO4(3-) to HCO3-/PO4(3-)-free Hepes buffered high K+/low Na+ media.(ABSTRACT TRUNCATED AT 250 WORDS)
J Mol Cell Cardiol 1986 Nov
PMID:Ca2+ transport systems mediating the high K+/low Na+-induced uptake of Ca2+ into rat atrium. 379 76

The study of the dynamics of enzyme segmental movement is of considerable importance in the understanding of the physics of the catalytic function of these macromolecules, which cannot be adequately described without introduction of intramolecular mobility of their polypeptide chains. At present high resolution [13C]NMR is mostly used as an effective and selective method for the observation of spectral and relaxation parameters that are sensitive to structure, conformation and local motion. The molecular dynamics of bovine carbonic anhydrase B (carbonate hydrolase EC. 4.2.1.1) in the native form was studied. Measurements of the relaxation parameters (T1, T2 and NOE) of the alpha-carbons of the polypeptide chain in two high magnetic fields (4.7 and 11.7 T) were carried out. The model-free approach of Lipari and Szabo to the interpretation of these experimental data show a satisfactory agreement between theory and experiment for these carbon nuclei if an internal degree of motion such as libration or restricted diffusion in a cone with angular amplitude in the 10 degrees less than theta less than or equal to 20 degrees range and an effective correlation time tau e approximately equal to 6 to 7 x 10(-11) S in addition to the tau R = 3 x 10(-8) S reorientation correlation time of the whole molecular is introduced.
Mol Biol (Mosk)
PMID:[Study of molecular dynamics of bovine carbonic anhydrase B by 13C-NMR in two strongly polarizing magnetic fields. I. Intramolecular mobility of polypeptide chains of the native enzyme]. 393 11

The development of erythrocytic stages of Plasmodium knowlesi separated from their host cells has been determined in terms of the capacity of the isolated organisms to carry out the synthesis and secretion of proteins. P. knowlesi trophozoites and schizonts were released from host cells by nitrogen decompression and cultivated in a medium consisting of 20 mM Na+; 120 mM K+; 1 mM Mg2+; no Ca2+; 100 mM Cl-; 20 mM HCO3-; 5 mM Hepes [pH 6.73], glucose, vitamins, amino acids and 10% fetal calf serum. The yield was about 97% intact parasites, judging by their ability to maintain a membrane potential, and these parasites had more than 80% the capacity of infected cells for nuclear replication and macromolecule biosynthesis. Pulse and pulse-chase labeling studies with [35S]methionine show that parasite-synthesized proteins with Mr 160 000, 140 000, 100 000 and 58 000 are exported from the parasite in soluble form. Proteins with Mr 140 000, 100 000, 58 000-60 000, 40 000 were recovered in a particulate fraction isolated from the parasite culture fluid. An Mr 62 000 protein synthesized in large amounts by isolated parasites during the last 2h of the developmental cycle, could not be detected in infected erythrocytes, and a minor early Mr 74 000 protein becomes prominent in free parasites but not infected cells toward the end of the developmental cycle. Parasite-synthesized proteins with Mr 230 000, 160 000, 140 000, 62 000, 58 000 and 45 000 were labeled by incubation with radioactive N-acetylglucosamine during short term incubation in vitro. About 80% of label incorporation occurred via N-glycosylation supported by dolichol derived from the blood, and about 20% via glycolytic intermediates.
Mol Biochem Parasitol 1985 Nov
PMID:Extracellular development of Plasmodium knowlesi erythrocytic stages in an artificial intracellular medium. 406 57

A pancreatic ribonuclease digest of (14)C-labeled tobacco necrosis virus RNA was fractionated according to charge by column chromatography. Individual fractions were dephosphorylated with alkaline phosphatase and rechromatographed. The fraction, originally containing oligonucleotides with seven negative charges, separated into two components corresponding to five (-5) and two negative charges (-2). The -5 fraction was derived from the internal oligonucleotides while the -2 fraction must have originated from a 5'-pyrophosphorylated terminal trinucleotide. The sequence of this terminal trinucleotide was determined by column chromatography on DEAE-cellulose in a triethyl ammonium carbonate gradient, using the appropriate markers. The radioactivity chromatographed with a (ApGp)U marker. The order of the Ap and Gp was determined after ribonuclease T(1) and alkaline phosphatase digestion. The radioactivity in the product chromatographed with an ApG marker. The 5'-terminus of tobacco necrosis virus RNA was therefore determined as ppApGpUp..., which is identical to the terminus of the RNA of its satellite virus as previously determined (J. Mol. Biol., 38, 59 (1968); Science, 160, 1452 (1968)). The 5' pyrophosphate in both viruses was probably formed by an in vivo enzymatic removal of a gamma-phosphate from a triphosphate, and its presence in both viruses suggested a common site of synthesis. The identity of the 5'-terminal sequences is considered not to be fortuitous and is discussed from the standpoint of their role as a recognition site for the virus-specific RNA replicase.
 ...
PMID:Identity of the 5'-terminal RNA nucleotide sequence of the satellite tobacco necrosis virus and its helper virus: possible role of the 5'-terminus in the recognition by virus-specific RNA replicase. 527 92

The presence of a subset of fast-transported proteins containing sulfate while lacking carbohydrate residues [Stone et al. (1983). J. Neurochem. 41:1085-1089] was confirmed by two-dimensional gel electrophoretic analysis of individual fast-transported proteins double-labeled with 35SO4 and [3H]mannose. Analysis by high-pressure liquid chromatography revealed that the sulfate moieties of these "sulfoproteins" are linked to tyrosine residues. Separation of fast-transported 35SO4-labeled proteins delivered to local regions of axon from proteins en route toward terminal regions demonstrated, on the basis of acid lability of tyrosine-bound sulfate, that the sulfoproteins were localized preferentially in the wavefront of fast-transported proteins. Analysis of individual sulfoproteins confirmed differential transport in that sulfoproteins were present at threefold greater amount in the wavefront than in material off-loaded to local regions of the axon. By contrast, nonsulfated species of molecular weights similar to those of the sulfoproteins were detected in nearly equal amounts in both regions of the transport profile. Treatment of nerve segments containing total 35SO4-labeled fast-transported proteins with sodium carbonate led to solubilization of half the protein-bound sulfate. Exposure of the solubilized proteins to mild acid resulted in the release of approximately 80% of the 35SO4 associated with this fraction. Two-dimensional gel patterns displaying carbonate releasable or nonreleasable fractions are consistent with the most abundantly labeled sulfoproteins being transported within membrane-bound organelles. In terms of apparent destination and subcellular compartmentalization, the sulfoproteins meet critical requirements for consideration as secretable fast-transported proteins.
Cell Mol Neurobiol 1984 Sep
PMID:Fast axonal transport of tyrosine sulfate-containing proteins: preferential routing of sulfoproteins toward nerve terminals. 608 52

The effect of fluphenazine and related phenothiazine and thioxanthene derivatives on beef heart soluble mitochondrial ATPase (EC 3.6.1.3) was studied under a precise control of the Mg2+-ATP equilibrium. These drugs were shown to be reversible, noncompetitive inhibitors with respect to the substrate (the Mg . ATP complex). The inhibition was found to be dependent on the concentration of free magnesium ions, although free Mg2+ was not essential for the interaction of the inhibitors with the enzymatic protein. Bicarbonate anions, which are known to antagonize the effect of free Mg2+ on the enzyme kinetics, also antagonized the drug-induced inhibition. Concentrations giving 50% inhibition of enzyme activity were in the micromolar range. Inhibitory potencies increased when the pH of the reaction mixture was lowered from 8.2 to 6.9. Cleland [The Enzymes (P. D. Boyer, ed.), Vol. II. Academic Press, New York, 1--65 (1970)] analysis of the inhibition, by means of slope and intercept replots, indicated that the inhibition was the result of the interaction with more than one drug molecule. All drugs tested afforded complete protection against the cold-induced inactivation of soluble mitochondrial ATPase. These results point to a specific mode of inhibition that mimics, in some respects, the action of the natural inhibitor protein of mitochondrial ATPase.
Mol Pharmacol 1982 Mar
PMID:Magnesium-dependent inhibition of beef heart soluble mitochondrial adenosine triphosphatase by tricyclic antipsychotics. 612 79

Net ionic flux and mucosal ultrastructure were examined following perfusion of the cat pancreatic duct with bicarbonate or sodium taurocholate solutions (5-40 mM). Taurocholate perfusion increased net Cl- gain, net HCO3- loss and net K+ gain and was associated with significant widening of lateral intercellular spaces and increased complexity of intercellular labyrinths. Increased perfusion pressure (30 mm Hg) did not affect flux or ultrastructure during perfusion with bicarbonate but increased net ion flux significantly during perfusion with 40 mM sodium taurocholate. Ultrastructural changes during perfusion of 40 mM taurocholate at increased pressure were not consistent but focal epithelial disruption and cell shedding were seen occasionally. The hypothesis is advanced that taurocholate perfusion triggers physiological transport mechanisms and may make the duct mucosa more vulnerable to other potentially harmful agents. The significance of these changes in the pathogenesis of acute pancreatitis in man remains uncertain and care must be exercised before extrapolating from observed net ion flux data in this animal model.
Virchows Arch B Cell Pathol Incl Mol Pathol 1983
PMID:Effect of bile salt perfusion and intraduct pressure on ionic flux and mucosal ultrastructure in the pancreatic duct of the cat. 613 94


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