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)

A minor fraction of the total ecto-type (E-type) ATPase activity of rat synaptosomes has been detected in immunoprecipitates of the neural cell adhesion molecule, NCAM, indicating that this either is an intrinsic enzymatic activity of NCAM or of an ATPase tightly associated to NCAM [Dzhandzhugazyan & Bock (1993) FEBS Lett. 336, 279-283]. We here demonstrate ATPase activity in preparations of the lipid-anchored as well as the transmembrane NCAM isoforms immunoisolated from transfected L-cells. A fraction of the E-type ATPase activity is spontaneously released from synaptosomes. Released material was fractionated by various chromatographic procedures and an extracellular fragment of NCAM was shown to co-elute with the major part of the enzymatic activity. Furthermore, it was shown that agarose-coupled NCAM-antibodies retained 85% of the ATPase activity released from synaptosomes after treatment with phosphatidylinositol-specific phospholipase C. These findings restricted the association or expression of the enzymatic activity to the extracellular part of NCAM. An affinity reagent, 5'-p-fluorosulfonylbenzoyl adenosine, FSBA, was shown to inhibit ATPase activity of immunoisolated NCAM, and incorporation of FSBA was detected in all three major NCAM isoforms (A, B, and C). An excess of ATP prevented both inactivation of the enzyme and affinity labeling of NCAM. Thus, NCAM contains an ATP-binding site, and this site is localized extracellularly and probably has the catalytic function. Binding of the substrate or FSBA protected a proteolytic cleavage site in NCAM localized close to the membrane presumably by induction of a local conformational change in NCAM, indicating a mechanism by which ATP may regulate NCAM adhesion and adhesion-triggered processes. A possible role of this mechanism in synaptic plasticity and memory consolidation is proposed.
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PMID:Demonstration of an extracellular ATP-binding site in NCAM: functional implications of nucleotide binding. 939 68

An extracellular ATPase (E-type ATPase) clone was isolated from a human brain cDNA library and sequenced. The transcript shows similarity to the previously published chicken smooth muscle and rat brain ecto-ATPase cDNAs, human CD39L1 cDNA (putative human ecto-ATPase), and mammalian CD39 (lymphoid cell activation antigen, ecto-apyrase, ATPDase, ATP-diphosphohydrolase) cDNAs. The full-length human brain cDNA encodes a 529 amino acid glycoprotein with a putative membrane spanning region near each terminus, with the majority of the protein found extracellularly. Expression of this clone in mammalian COS-1 cells yielded NaN3-sensitive ATPase and ADPase activity detectable both on intact cells and cell membrane preparations. The nucleotide hydrolysis ratio of the expressed protein is approx. 2.75:1 (ATPase:ADPase activity), classifying it as an ecto-apyrase. However, this hydrolysis ratio is intermediate between that observed for the ecto-ATPases and the CD39 ecto-apyrases (L. Plesner, Int. Rev. Cytol. 158 (1995) 141-214). Quantitative analyses of amino acid identities and similarities between this ecto-apyrase and other vertebrate E-type ATPases suggest that this human brain enzyme is nearly equally related to the ecto-ATPases and the CD39s, and phylogenetic analysis suggests that it could be an ancestral enzyme from which both ecto-ATPases and CD39 ecto-apyrases are derived.
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PMID:Cloning, sequencing, and expression of a human brain ecto-apyrase related to both the ecto-ATPases and CD39 ecto-apyrases1. 967 46

A human brain E-type ATPase (HB6 ecto-apyrase) was subjected to site-directed mutagenesis to assess the functional significance of two highly conserved tryptophan residues (Trp 187 and Trp 459), the only two tryptophans conserved in nearly all E-type ATPases. Mutation of tryptophan 187 to alanine yielded a poorly expressed ecto-apyrase completely devoid of nucleotidase activity. Immunolocalization of the W187A mutant in mammalian COS cells showed a cellular distribution clearly different from that of the wild-type enzyme, with the majority of the immunoreactivity concentrated in the interior of the cell. Unlike the wild-type enzyme, this mutant did not bind the nucleotide analogue Cibacron Blue and was sensitive to proteolytic digestion by chymotrypsin. These results suggest alteration of the tertiary structure, causing the enzyme to be improperly folded and retained within the cell. In contrast, mutation of tryptophan 459 to alanine resulted in an ecto-apyrase with enhanced NTPase activity, but diminished NDPase activity. Immunolocalization of this active mutant ecto-apyrase revealed a cellular pattern similar to that of the wild-type enzyme, distributed along the cell periphery and in cell processes. Coupling this active W459A mutation to a previously described mutation (D219E) resulted in an enzyme which preferentially hydrolyzes nucleoside triphosphates over diphosphates. The D219E/W459A double mutant had an ATPase:ADPase ratio of 11:1 and a UTPase:UDPase ratio of 148:1. In addition, the double mutant is substantially less sensitive to inhibition by azide, a more potent inhibitor of ecto-apyrases than ecto-ATPases. Thus, mutation of only two amino acids of an E-type ATPase essentially converts an ecto-apyrase to an ecto-NTPase.
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PMID:Mutagenesis of two conserved tryptophan residues of the E-type ATPases: inactivation and conversion of an ecto-apyrase to an ecto-NTPase. 1023 36

Lesch-Nyhan disease is caused by a deficiency of the purine salvage enzyme, hypoxanthine phosphoribosyl transferase (HPRT). The link between HPRT deficiency and the neuropsychiatric symptoms is unknown. In rat B103 neuroblastoma cell membranes and mouse Neuro2a neuroblastoma cell membranes, nucleoside 5'-triphosphatase (NTPase) activity is substantially reduced, whereas in fibroblast membranes from HPRT knock-out mice, NTPase activity is increased. Candidate genes for these NTPase activity changes are ecto-nucleoside 5'-triphosphate diphosphohydrolases (NTPDases). Therefore, we studied expression of NTPDases in B103 cells, Neuro2a cells and skin fibroblasts by reverse transcriptase polymerase chain reaction and restriction enzyme digestion of amplified cDNA fragments. In B103 cells, expression of NTPDases 1, 3 and 6 decreased, whereas expression of NTPDases 4 and 5 increased in HPRT deficiency. In Neuro2a cells, expression of NTPDases 3-6 increased in HPRT deficiency. In fibroblasts, NTPDase 3 expression decreased, and expression of NTPDases 4-6 increased in HPRT deficiency. Collectively, there are complex decreases and increases in NTPDase isoform expression in HPRT deficiency that depend on the specific cell type and species studied. These changes in NTPDase expression may reflect an (insufficient) attempt of cells to compensate for the changes in nucleotide metabolism caused by HPRT deficiency.
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PMID:Complex changes in ecto-nucleoside 5'-triphosphate diphosphohydrolase expression in hypoxanthine phosphoribosyl transferase deficiency. 1745 84