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:3.6.1.3 (ATPase)
65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We recently demonstrated that the Alzheimer's beta-amyloid precursor protein (APP) is internalized from the axonal cell surface. In this study, we use biochemical and cell biological methods to characterize endocytotic compartments that participate in trafficking of APP in central neurons. APP is present in presynaptic clathrin-coated vesicles purified from bovine brain, together with the recycling synaptic vesicle integral membrane proteins synaptophysin, synaptotagmin, and SV2. In contrast, APP is largely excluded from synaptic vesicles purified from rat brain. In primary cerebellar macroneurons, cell-surface APP is internalized with recycling synaptic vesicle integral membrane proteins but is subsequently sorted away from synaptic vesicles and transported retrogradely to the neuronal soma. Internalized APP partially co-localizes with rab5a-containing compartments in axons and with V-ATPase-containing compartments in both axons and neuronal soma. These results provide direct biochemical evidence that an obligate sorting compartment participates in the regeneration of synaptic vesicles during exo/endocytotic recycling at nerve terminals but do not preclude concurrent "kiss-and-run" recycling. Moreover, APP is now, to our knowledge, the first demonstrated example of an axonal cell-surface protein that is internalized with recycling synaptic vesicle membrane proteins but is subsequently sorted away from synaptic vesicles.
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PMID:Trafficking of cell-surface beta-amyloid precursor protein: evidence that a sorting intermediate participates in synaptic vesicle recycling. 898 43

Soluble N-ethylmaleimide-sensitive factor attached protein (SNAP) receptor (SNARE) mechanisms are thought to be involved in two important processes in axonal growth cones: (1) membrane expansion for axonal growth and (2) vesicular membrane fusion for mature synaptic transmission. We investigated the localization and interactions among the proteins involved in SNARE complex formation in isolated growth cone particles (GCP) from forebrain. We demonstrated that the SNARE complex is present in GCPs morphologically without synaptic vesicles (SVs) and associated with growth cone vesicles. However, the apparently SV-free GCP was lacking in the regulatory mechanisms inhibiting SNARE complex formation proposed in SV fusion, i.e., the association of synaptotagmin with the SNARE complex, and vesicle-associated membrane protein (VAMP)-synaptophysin complex formation. The core components of the SNARE complex (syntaxin, SNAP-25, and VAMP) accumulated for several days before postnatal day 7, when SVs first appeared, and preceded the accumulation of marker proteins such as synaptophysin, SV2, and V-ATPase. Our present results suggest that the SNARE mechanism for vesicular transmitter release is not fully functional in growth cones before the appearance of SVs, but the SNARE mechanism is working for membrane expansion in growth cones, which supports our recent report. We concluded that the regulation of the SNARE complex in growth cones is different from that in mature presynaptic terminals and that this switching may be one of the key steps in development from the growth cone to the presynaptic terminal.
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PMID:The soluble N-ethylmaleimide-sensitive factor attached protein receptor complex in growth cones: molecular aspects of the axon terminal development. 900 87

Physophilin is an oligomeric protein that binds the synaptic vesicle protein synaptophysin constituting a complex that has been hypothesized to form the exocytotic fusion pore. Microsequencing of several physophilin peptides putatively identified this protein as the Ac39 subunit of the V-ATPase. Ac39 has recently been shown to be present in a synaptosomal complex which, in addition to synaptophysin, includes the bulk of synaptobrevin II, and subunits c and Ac115 of the V0 sector of the V-ATPase. We have cloned physophilin from mouse brain and found a differential region of 12 amino acids when compared with the previously reported sequence of Ac39 from bovine adrenal medulla. RT-PCR cloning from the bovine adrenal medulla demonstrates that sequencing errors occurred in the previous cloning study, and shows that the amino acid sequences of physophilin and Ac39 are completely identical. In situ hybridization in rat brain reveals a largely neuronal distribution of Ac39/physophilin mRNA which spatio-temporally correlates with those of subunit c and synaptophysin. Immunohistochemical analysis shows that Ac39/physophilin is mostly concentrated in the neuropil with a pattern identical to subunit A and very similar to synaptophysin. Double-labelling immunofluorescence shows a complete colocalization of Ac39/physophilin with subunit A and a partial colocalization with synaptophysin in the neuropil. Our findings bring anatomical support for the in vivo occurrence of the synaptophysin-Ac39/physophilin interaction and further suggest a coordinated transcription of V-ATPase and synaptophysin genes. A putative role of Ac39/physophilin in the inactivation of the V-ATPase by disassembly of its V1 sector is also discussed.
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PMID:Brain Ac39/physophilin: cloning, coexpression and colocalization with synaptophysin. 975 84

Vesicular monoamine transporters (VMATs) are involved in chemical transduction in monoaminergic neurons and various endocrine cells through the storage of monoamines in secretory vesicles. Mammalian pinealocytes contain more 5-hydroxytryptamine (5-HT) than any other cells and are expected to contain VMAT, although no information is available so far. Upon the addition of ATP, radiolabeled 5-HT was taken up by a particulate fraction prepared from cultured rat pinealocytes. The 5-HT uptake was inhibited significantly by bafilomycin A1 (an inhibitor of vacuolar H+-ATPase), 3,5-di-tert-butyl-4-hydroxybenzylidenemalononitrile (a proton conductor), or reserpine (an inhibitor of VMAT). RT-PCR analysis suggested that VMAT type 1 (VMAT1), but not type 2, is expressed. Antibodies against VMAT1 recognized a single polypeptide with an apparent molecular mass of approximately 55 kDa, and specifically immunostained pinealocytes. VMAT1 immunoreactivity was high in the vesicular structures in the varicosities of long branching processes and was associated with 5-HT, but not with synaptophysin, a marker protein for microvesicles. The 5-HT immunoreactivity in the long branching processes disappeared upon incubation with reserpine. These results indicate that 5-HT, at least in part, is stored in vesicles other than microvesicles in pinealocytes through a mechanism similar to that of various secretory vesicles.
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PMID:Vesicular monoamine transporter 1 is responsible for storage of 5-hydroxytryptamine in rat pinealocytes. 1058 16

Ca2+/calmodulin-dependent protein kinase II is thought to participate in M3 muscarinic receptor-mediated acid secretion in gastric parietal cells. During acid secretion tubulovesicles carrying H+/K+-ATPase fuse with the apical membrane. We localized Ca2+/calmodulin-dependent protein kinase II from highly purified rabbit gastric tubulovesicles using Ca2+/calmodulin-dependent protein kinase II isoform-specific antibodies, in vitro phosphorylation and pharmacological inhibition of Ca2+/calmodulin-dependent protein kinase II activity by the potent Ca2+/calmodulin-dependent protein kinase II inhibitor KN-62. The presence of Ca2+/calmodulin-dependent protein kinase II in tubulovesicles was shown by immunoblot detection of both Ca2+/calmodulin-dependent protein kinase II-gamma (54 kDa) and Ca2+/calmodulin-dependent protein kinase II-delta (56.5 kDa). The immunoprecipitated Ca2+/calmodulin-dependent protein kinase II from tubulovesicles showed Ca2+/calmodulin-dependent protein kinase activity by phosphorylating autocamtide-II, a specific synthetic Ca2+/calmodulin-dependent protein kinase II substrate. KN-62 inhibited the in vitro autophosphorylation of tubulovesicle-associated Ca2+/calmodulin-dependent protein kinase II (IC50 = 11 nM). During the search for potential Ca2+/calmodulin-dependent protein kinase II substrates we identified different proteins associated with tubulovesicles, such as synaptophysin and beta-tubulin immunoreactivity, which were identified using specific antibodies. These targets are known to participate in intracellular membrane traffic. Ca2+/calmodulin-dependent protein kinase II is thought to play an important role in regulating tubulovesicular motor activity and therefore in acid secretion.
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PMID:Ca2+/calmodulin-dependent protein kinase II isoenzymes gamma and delta are both present in H+/K+-ATPase-containing rabbit gastric tubulovesicles. 1058 99

Flow cytometry techniques, usually employed to characterize cellular populations, are reported here to be a valuable tool to approach the study of subcellular organelle functioning. Chromaffin granules rendered fluorescent by using an antibody against their membrane protein, synaptophysin, are detectable by flow cytometry. Moreover, these storage granules are able to transport the fluorescent ATP analogue, epsilon-ATP (1,N6-ethenoadenosine 5'-triphosphate), and the resulting granular fluorescence increase can also be followed by this technique. The saturation studies show a non-hyperbolic kinetic behaviour, with a two step curve. The K0.5 values were 0.26 and 2.5 mM and Hill numbers 1 and 6 respectively. In addition, an unexpected granular size increase, which was dependent on the epsilon-ATP concentration, occurred together with the fluorescence increase. Other nucleotide triphosphate substrates of V-ATPase, such as ATP or GTP, but not the non-hydrolyzable analogue ATP gamma S (adenosine 5'-O-(3-thiotriphosphate), mimic this effect, which exhibited sigmoidal saturation curves with K0.5 values of 1.8 and 3.1 mM for ATP and epsilon-ATP respectively. The V-ATPase inhibitors, suramin, EGTA or EDTA significantly reduced the granular size increase in the presence of ATP. Extragranular addition of noradrenaline has no effect by itself on the granular size, but significantly reduced the granular size increase induced by ATP. This effect was reversed by the amine transport inhibitor reserpine. The granular size increase induced by ATP was more effective in the presence of Cl- than Br- or I-. Moreover, no increase occurred in the presence of F- or acetate. The Cl- channel blockers were poorly effective, and only 2-(phenylamino)-benzoic acid (DPC) exhibited an effect on the ATP-induced granular size increase.
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PMID:Studies of chromaffin granule functioning by flow cytometry: transport of fluorescent epsilon-ATP and granular size increase induced by ATP. 1063 62

Pancreatic islet cells express receptors and transporters for L-glutamate and are thus believed to use L-glutamate as an intercellular signaling molecule. However, the mechanism by which L-glutamate appears in the islets is unknown. In the present study, we investigated whether L-glutamate is secreted through exocytosis by alphaTC6 cells (clonal mouse pancreatic alpha-cells). An appreciable amount of L-glutamate was released from cultured cells after the addition of KCl or A23187 in the presence of Ca2+ and 10 mmol/l glucose in the medium. The KCl-induced glutamate release was significantly reduced when assayed in the absence of Ca2+ or when the cells were pretreated with EGTA-AM. The KCl-induced Ca2+-dependent glutamate release was inhibited approximately 40% by voltage-gated Ca2+ channel blockers, such as nifedipine at 20 micromol/l. The degree of KCl-induced Ca2+-dependent glutamate release was correlated with an increase in intracellular [Ca2+], as monitored by fura-2 fluorescence. Botulinum neurotoxin type E inhibited 55% of the KCl-induced Ca2+-dependent glutamate release, followed by specific cleavage of 25 kDa synaptosomal-associated protein. Furthermore, bafilomycin A1, a specific inhibitor of vacuolar H+-ATPase, inhibited 40% of the KCl-induced Ca2+-dependent glutamate release. Immunoelectronmicroscopy with antibodies against synaptophysin, a marker for neuronal synaptic vesicles and endocrine synaptic-like microvesicles, revealed a large number of synaptophysin-positive clear vesicles in cells. Digitonin-permeabilized cells took up L-glutamate only in the presence of MgATP, which is sensitive to bafilomycin A1 or 3,5-di-tert-butyl-4-hydroxybenzylidene-malononitrile (a proton conductor) but insensitive to either oligomycin or vanadate. From these results, it was concluded that alphaTC6 cells accumulate L-glutamate in the synaptophysin-containing vesicles in an ATP-dependent manner and secrete it through a Ca2+-dependent exocytic mechanism. The Ca2+-dependent glutamate release was also triggered when cells were transferred in the medium containing 1 mmol/l glucose, suggesting that low glucose treatment stimulates the release of glutamate. Our results are consistent with the idea that L-glutamate is secreted by alpha-cells through Ca2+-dependent regulated exocytosis.
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PMID:Ca2+-dependent exocytosis of L-glutamate by alphaTC6, clonal mouse pancreatic alpha-cells. 1133 3

The endoplasmic reticulum (ER) is the major membranous component present throughout the axon. Although other membranous structures such as synaptic vesicles are known to move via fast axonal transport, the dynamics of ER in the axon still remains unknown. To study the dynamics of ER in the axon, we have directly visualized the movement of two ER-specific membrane proteins, the sarcoplasmic/endoplasmic reticulum calcium-ATPase and the inositol 1,4,5-trisphosphate receptor, both of which were tagged with green fluorescence protein (GFP) and expressed in cultured chick dorsal root ganglion neurons. In contrast to GFP-tagged synaptophysin that moved as vesicles at 1 microm/sec predominantly in the anterograde direction in the typical style of fast axonal transport, the two ER proteins did not move in a discrete vesicular form. Their movement determined by the fluorescence recovery after photobleaching technique was bi-directional, 10-fold slower (approximately 0.1 microm/sec), and temperature-sensitive. The rate of movement of ER was also sensitive to low doses of vinblastine and nocodazole that did not affect the rate of synaptophysin-GFP, further suggesting that it is also distinct from the well-documented movement of membranous vesicles in its relation with microtubules.
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PMID:Movement of endoplasmic reticulum in the living axon is distinct from other membranous vesicles in its rate, form, and sensitivity to microtubule inhibitors. 1149 58

A preparative proteomic approach, involving liquid phase isoelectric focusing (IEF) in combination with one-dimensional electrophoresis and electroelution followed by mass spectrometry and database searches, was found to be an important tool for identifying low-abundant proteins (microgram/L) in human cerebrospinal fluid (CSF) and membrane proteins in human frontal cortex. Several neuron-related proteins, such as amyloid precursor-like protein, chromogranins A and B, glial fibrillary acid protein, beta-trace, transthyretin, ubiquitin, and cystatin C, were identified in CSF. Several types of proteins were also characterized from a detergent-solubilized human frontal cortex homogenate including membrane proteins such as synaptophysin, syntaxin and Na+/K+ ATPase. One-third of the identified proteins have not previously been identified in human CSF or human frontal cortex using proteomic techniques. The absence of these proteins in two-dimensional electrophoresis maps might be due to insufficient amounts or low solubility. The advantages of using preparative liquid phase electrophoretic separations for identifying proteins from complex biological mixtures are speed of analysis, high loadability in the IEF separation, nondiscrimination of membrane proteins or low abundance proteins, yielding sufficient amounts for characterization by mass spectrometry. The use of this strategy in proteome studies of CSF/brain tissue is expected to offer new perspectives in studies of the pathology of neurodegenerative diseases, and reveal new potential markers for brain disorders.
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PMID:Proteome studies of human cerebrospinal fluid and brain tissue using a preparative two-dimensional electrophoresis approach prior to mass spectrometry. 1168 Aug 89

Synaptic-like microvesicles (SLMVs) are morphological and functional equivalents of neuronal synaptic vesicles, and are responsible for the storage and secretion of classical neurotransmitters in various endocrine cells. Vacuolar H+-ATPase acidifies the internal space of these organelles and provides a driving force for the uptake of neurotransmitters. Thus, the luminal pH is an important determinant of the function of SLMVs, although its value in living cells is unknown. Here, we determined the luminal pH of SLMVs in living rat pinealocytes by means of an immunoelectronmicroscopic procedure basedon the distribution of an amphipathic amine, 3-(2,4-dinitroanilino)-3'-amino-N-methyldipropylamine (DAMP). Use of double-labeling techniques with antibodies against 2,4-dinitrophenol for DAMP and synaptophysin for SLMVs, and of frozen ultrathin sections enabled us to determine the number of immunogold particles for DAMP per microm2 of SLMVs. Using the density of gold particles, the luminal pH of SLMVs was calculated to be 5.11 +/- 0.01. Treatment with either 1 microm bafilomycin A1, a specific inhibitor of vacuolar H+-ATPase, or 50 mm ammonium chloride, a dissipater of the transmembrane pH gradient, increased the luminal pH to 6.04 +/- 0.07 and 6.05 +/- 0.11, respectively. Simultaneously, the lysosomal pH was found to be 5.14 +/- 0.07, which increased to 5.77 +/- 0.09 and 5.93 +/- 0.13 with bafilomycin A1 and ammonium chloride, respectively. It is concluded that the luminal pH of SLMVs is comparable to that of lysosomes in vivo.
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PMID:The internal pH of synaptic-like microvesicles in rat pinealocytes in culture. 1215 93


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