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:3.1.4.1 (phosphodiesterase)
18,767 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The glutamine synthetase (EC 6.3.1.2) from the N2-fixing bacterium Azotobacter vinelandii was purified to homogeneity by heat treatment, ammonium sulfate precipitation and ion-exchange chromatography. The following molecular parameters were determined: molecular weight 640 000, subunit molecular weight 53 000, partial specific volume 0.710 cm3/g, isoelectric point 4.6, amino acid composition. Most of the molecules are composed of 12 identical subunits but active oligomers of other degrees of polymerization, apparently aggregates with 8, 10 and 24 subunits, were also detected to a lesser extent. The enzymatic activity is regulated via adenylylation-deadenylylation cycles: liberation of AMP was detected upon treatment of the adenylylated form with phosphodiesterase along with a change in the catalytic properties. Adenylylation in vivo is specifically induced by high extracellular ammonia levels. The Km values for the Mg2+-dependent formation of glutamine were independent of the degree of adenylylation for glutamate and ATP, but varied for ammonia. Furthermore the catalytic activity is regulated by several nitrogenous feedback inhibitors. The degree of inhibition in some cases was dependent on the substrate concentrations: the sensitivity towards glycine, alanine and serine decreased with a decreasing ammonia level, while the sensitivity towards ADP or AMP increased with a decreasing ATP concentration. Part of the enzyme (about 30%) seems to be attached to the plasma membrane while the main fraction is found in the cytosol.
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PMID:The glutamine synthetase from Azotobacter vinelandii: purification, characterization, regulation and localization. 2 57

Activity, ratio and summary content of cyclic AMP enzymes, adenylate cyclase and phosphodiesterase varied depending on growth conditions of phototrophic bacteria (Rhodospirillum rubrum and Rhodopseudomonas palustris). It suggests, that membrane-bound and soluble enzymes carry different functions. The increase of adenylate cyclase under chaning growth conditions was usually accompanied by the increase of phosphodiesterase. Sharp increase of both enzymes activity was observed when bacteria were growth in aerobic conditions. The activity of both enzymes in chromatophores was 2.8-fold higher when bacteria were grown in the light in anaerobic conditions, than in chromatophores of bacteria grown under stationary aerobic conditions in the light. It is suggested that 3':5' AMP can participate in autotrophic carbon assimilation or in the synthesis of pigments and other components of bacterial photosynthetizing apparatus. Substitution of NH4+ into NO3- and glutamate under the growing of R. rubrum in anaerobic conditions in the light resulted in the increase of the enzymes activities, which is the evidence of possible role of 3':5' AMP in mineral nitrogen uptake and nitrogen fixation. Glutamate concentration of 4 g/l stimulated the enzymes both in vivo and in vitro. The data obtained suggest that 3':5' AMP can carry multiple functions, participating in regulation of a number of metabolic processes in photorophic bacteria.
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PMID:[Effect of growth conditions on the activity of the enzymes of cyclic 3':5'-AMP synthesis and decay in phototrophic bacteria]. 20 63

A cyclic nucleotide-binding phosphohydrolase that possesses both a phosphomonoesterase and a phosphodiesterase catalytic function has been partially purified from Aspergillus nidulans. The enzyme hydrolyzes both p-nitrophenylphosphate and bis-(p-nitrophenyl)-phosphate. o'-Nucleoside monophosphates are the best physiological phosphomonesterase substrates but 5'- and 2'-nucleoside monophosphates are also hydrolyzed. The enzyme catalyzes the hydrolysis of adenosine 5'-triphosphate, adenosine 5'-diphosphate, and 2',3'- and 3'5'-cyclic nucleotides, but not of ribonucleic acid, deoxyribonucleic acid, or nicotinamide adenine dinucleotide. The enzyme has acid pH optima and is not activated by divalent cations. Nucleosides and nucleotides inhibit the enzyme. Cyclic nucleotides are competitive inhibitors of the phosphodiesterase-phosphomonoesterase. The enzyme can occur extracellularly. The phosphodiesterase-phosphomonoesterase is present at high levels in nitrogen-starved mycelium, and it is strongly repressed during growth in media containing ammonium or glutamine and weakly repressed during growth in glutamate-containing medium. Experiments with various area mutants show that this regulatory gene is involved in the control of the enzyme. No evidence for regulation of the enzyme by carbon or phosphorus starvation has been found.
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PMID:Enzymology and genetic regulation of a cyclic nucleotide-binding phosphodiesterase-phosphomonoesterase from Aspergillus nidulans. 24 43

The dermal cells in grey, xanthic, and white goldfish integuments were cytochemically characterized for the following enzymatic activities: tyrosinase, DOPA-oxidase, cytochrome oxidase, monoamine oxidase, peroxidase, non-specific esterase, cholinesterase, NAD-diaphorase, NADP-diaphorase, aryl sulfatase, nucleotide phosphodiesterase, beta-glucuronidase, acid phosphatase, alkaline phosphatase, adenosine triphosphatase, thiamine pyrophosphatase, glucose-6-phosphatase, aldolase, as well as succinate, malate, isocitrate, glutamate, glucose-6-phosphate, 6-phosphogluconate, alpha-glycerophosphate, alcohol, lactate, and beta-hydroxybutyrate dehydrogenases. It was found that the epidermis was a significant barrier to the access of cytochemical reaction substrates. Removal of the epidermal barrier provided dermal cell localizations of enzymatic activities which were reproducible. Further, alterations in reaction times and temperatures from the mammalian methodology provided conditions fe various integumental cells were compared for possible interrelationships. The basic foundations for future work with the dermis of poikilothermic vertebrates on an experimental basis were established. In addition, a previously undescribed non-pigmented dermal cell, the "x"-cell, was found to have enzymatic characteristics similar to both melanophores and lipophores. The "x"-cell may be the common precursor of both types of pigment cells.
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PMID:Cytochemical characterization of goldfish (Carassius auratus L.) dermis with special reference to the pigment cells. 82 86

1. The potassium currents evoked by glutamate agonists on isolated and identified neurones of molluscan pedal ganglia were investigated using the voltage clamp technique. 2. Glutamate responses were not modified by increasing intracellular cyclic nucleotide concentrations (treatment with 8-Br-cAMP, 8-Br-cGMP, forskolin and/or the phosphodiesterase inhibitor isobutylmethylxantine, IBMX), whereas inward-going currents induced by the nucleotides were observed. It follows that glutamate currents are independent of intracellular cyclic nucleotide control. 3. Protein kinase C activation with phorbol esters or oleoylacetylglycerol induced a slowly developing outward current and reduced glutamate response amplitude. Staurosporine itself did not affect the glutamate responses but completely prevented the effects of phorbol esters and oleoylacetylglycerol. This indicated that protein kinase C was not involved in the transduction mechanism for the potassium component of the glutamate response. 4. The possible involvement of inositol-1,4,5-trisphosphate seems to be improbable because the glutamate responses were independent of intracellular calcium concentration. Intracellular injection of calcium buffer BAPTA, failed to affect any of the glutamate currents, although it effectively blocked the after-hyperpolarization following directly evoked action potentials. 5. Nordihydroguaiaretic acid (NDGA) and indomethacin, inhibitors of the lipoxygenase and cyclo-oxygenase pathways of arachidonic acid metabolism, correspondingly, did not change the glutamate responses of these neurones. 6. The failure to demonstrate the involvement of any known secondary messenger systems in glutamate response transduction favours two assumptions: (1) the receptor-G protein complex controls the potassium channel directly; or (2) some still unknown transduction system is used.
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PMID:Transduction mechanism for glutamate-induced potassium current in neurones of the mollusc Planorbarius corneus. 136 43

1. Intracellular recordings were made from CA3 hippocampal neurones in vitro, during the first ten days of postnatal life and in adulthood. 2. Repeated (three to six) applications of N-methyl-D-aspartate (NMDA), in the presence of tetrodotoxin (TTX, 1-3 microM) and K+ channel blockers (tetraethylammonium chloride or bromide (TEA), 10 mM, and Cs+, 2 mM; or 4-aminopyridine (4-AP), 30-50 microM, and Cs+, 2 mM) induced in neonatal but not in adult neurones, periodic inward currents (PICs) which persisted for several hours after the last application of NMDA. 3. PICs which were due to non-specific cation currents had a frequency of 0.10 +/- 0.04 Hz, and an amplitude of 1.1 +/- 0.28 nA at holding potentials between -40 and -50 mV. The amplitude was a linear function of the membrane potential over the range -70 to +20 mV. They reversed polarity at 4.1 +/- 9.8 mV. 4. K+ channel blockers alone failed to induce PICs. Repeated (three to six) brief applications of high (12 mM) K+ medium also induced PICs. The frequency and amplitude of K(+)-induced PICs were however considerably reduced by concomitant applications of the NMDA receptor antagonist D,L-3-[( +/- )-2-carboxypiperazin-4-yl-]propyl-1-phosphonic acid (CPP, 20 microM). PICs could be induced also by caffeine (1 mM) in the presence of the phosphodiesterase inhibitor 3-isobutyl-1-methyl-xanthine (IBMX, 200 microM), TTX, TEA and Cs+. 5. Intracellular injection of the calcium chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) did not prevent the induction of PICs by NMDA. However PICs were blocked by removal of the external calcium and by the calcium antagonists cobalt (2 mM) and cadmium (50 microM). 6. In spite of blockade of propagated synaptic activity by TTX, PICs were synchronous in a pair of intracellularly recorded cells. They were also synchronous with extracellular spikes recorded by electrodes located into stratum pyramidal or stratum radiatum. 7. Once established, PICs were unaffected by NMDA receptor antagonists D(-)2-amino-5-phosphonovaleric acid (AP-5, 50 microM), CPP (20 microM) and the NMDA channel blocker ketamine (10 microM). They were reversibly blocked by the broad spectrum excitatory amino acid antagonist kynurenic acid (1 mM) and by the selective non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM). 8. It is concluded that PICs are generated in neonatal neurones by a synchronous, pulsatile release of glutamate from presynaptic nerve terminals, secondary to oscillations in intracellular calcium.
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PMID:Persistent pulsatile release of glutamate induced by N-methyl-D-aspartate in neonatal rat hippocampal neurones. 167 21

Transmitter release from photoreceptors is decreased by light, resulting in a conductance increase in depolarizing bipolar cells. Addition of exogenous cGMP through a patch pipette to depolarizing bipolar cells from slices of dark-adapted tiger salamander retina resulted in an enhancement of the light response. This enhancement was blocked by GTP-gamma-S and dipyridamole, an inhibitor of phosphodiesterase. GTP-gamma-S and dipyridamole also blocked responses to exogenously applied 2-amino-4-phosphonobutyrate (APB), the glutamate agonist selective for this receptor. These data support the hypothesis that the postsynaptic receptor is linked via a G protein to a phosphodiesterase. The binding of glutamate or APB to the receptor suppresses a cGMP-activated current by increasing the rate of cyclic nucleotide hydrolysis.
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PMID:cGMP-gated conductance in retinal bipolar cells is suppressed by the photoreceptor transmitter. 168 33

Depolarizing bipolar cells (DBCs) of the retina are the only neurons in the vertebrate central nervous system known to be hyperpolarized by the neurotransmitter glutamate. Both glutamate and its analogue L-2-amino-4-phosphonobutyrate (APB) hyperpolarize DBCs by decreasing membrane conductance. Furthermore, glutamate responses in DBCs slowly decrease during whole-cell recording, suggesting that the response involves a second messenger system. Here we report that intracellular cyclic GMP or GTP activates a membrane conductance that is suppressed by APB, resulting in an enhanced APB response. In the presence of GTP-gamma-S, APB causes an irreversible suppression of the conductance. Inhibitors of G-protein activation or phosphodiesterase activity decrease the APB response. Thus, the DBC glutamate receptor seems to close ion channels by increasing the rate of cGMP hydrolysis by a G protein-mediated process that is strikingly similar to light transduction in photoreceptors.
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PMID:Suppression by glutamate of cGMP-activated conductance in retinal bipolar cells. 169 13

Whole-cell patch-clamp recordings were obtained from light-responsive on-bipolar cells in retinal slices of the dogfish. Inclusion of the G-protein activator, GTP gamma S, in the intracellular patch solution mimicked the action of glutamate, inducing an increase in net outward current (interpreted as a decrease in inward current), a decrease in membrane conductance and block of light responses. Cyclic GMP (cGMP) in the patch pipette increased inward current and membrane conductance, and blocked light responses. Cyclic AMP had no effect. IBMX, a phosphodiesterase inhibitor, produced the same effect as cGMP, suggesting the presence of a cGMP phosphodiesterase in rod bipolar cells. These results indicate that the glutamate receptors of on-bipolar cells are coupled via a G-protein to regulate intracellular cGMP, which, in turn, results in the opening of sub-synaptic membrane channels. The similarity to phototransduction is striking, and the proposed scheme would account for the high gain in transmission of rod signals to on-bipolar cells.
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PMID:Glutamate receptors of rod bipolar cells are linked to a cyclic GMP cascade via a G-protein. 170 97

Clonal lines of murine neuroblastoma (NBP2) and rat glioma (C6) were used to investigate the effects of methylmercuric chloride (CH3HgCl). Glioma cells were more sensitive to CH3HgCl than NB cells on the criterion of growth inhibition, but these cells were equally sensitive to inorganic mercury (HgCl1), Tri-n-butyl lead acetate and acrylamide on the same criterion. Alpha-tocopherol, alpha-tocopheryl++ succinate and inhibitors of cAMP phosphodiesterase protected glioma cells against the growth-inhibitory effect of CH3HgCl, but they failed to protect NB cells in culture. Glioma factors, sodium ascorbate, non-inhibitory concentrations of prostaglandins E1 (PGE1), and glutamate enhanced the growth-inhibitory effect of CH3HgCl on both NB and glioma cells in culture. The levels of certain specific cAMP-dependent and -independent protein phosphorylations appear to be very sensitive to CH3HgCl, and can be altered in both cell types by concentrations of CH3HgCl which do not affect growth or morphology of these cells.
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PMID:New opportunities with neuronal cultures to study the mechanisms of neurotoxic injuries. 174 37


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