Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P50583 (asymmetrical)
 12,197 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The P1P4-bis(5'-nucleosidyl) tetraphosphate asymmetrical-pyrophosphohydrolase from encysted embryos of the brine shrimp Artemia has been purified over 11,000-fold to homogeneity. Anion-exchange chromatography resolves two major species with very similar properties. The enzyme is a single polypeptide of Mr 17,600 and is maximally active at pH 8.4 and 2 mM-Mg2+. It is inhibited by Ca2+ (IC50 = 0.9 mM with 2 mM-Mg2+) but not by Zn2+ ions. It preferentially hydrolyses P1P4-bis(5'-nucleosidyl) tetraphosphates, e.g. P1P4-bis(5'-adenosyl) tetraphosphate (Ap4A) (kcat. = 12.7 s-1; Km = 33 microM) and P1P4-bis(5'-guanosyl) tetraphosphate (Gp4G) (kcat. = 6.2 s-1; Km = 5 microM). With adenosine 5'-P1-tetraphospho-P4-5"'-guanosine (Ap4G) as substrate, there is a 4.5-fold preference for AMP and GTP as products and biphasic reaction kinetics are observed giving Km values of 4.7 microM and 34 microM, and corresponding rate constants of 6.5 s-1 and 11.9 s-1. The net rate constant for Ap4G hydrolysis is 7.6 s-1. The enzyme will also hydrolyse nucleotides with more than four phosphate groups, e.g. Ap5G, Ap6A and Gp5G are hydrolysed at 25%, 18% and 10% of the rate of Ap4A respectively. An NTP is always one of the products. Ap2A and Gp2G are not hydrolysed, while Ap3A and Gp3G are very poor substrates. When the enzyme is partially purified from embryos and larvae at different stages of development by sedimentation through a sucrose density gradient, its activity increases 3-fold during the first 12 h of pre-emergence development. This is followed by a slow decline during subsequent larval development. The similarity of this enzyme to other asymmetrical-pyrophosphohydrolases suggests that it did not evolve specifically to degrade the large yolk platelet store of Gp4G which is found in Artemia embryos, but that it probably serves the same general function in bis(5'-nucleosidyl) oligophosphate metabolism as in other cells.
 ...
PMID:Characterization of the bis(5'-nucleosidyl) tetraphosphate pyrophosphohydrolase from encysted embryos of the brine shrimp Artemia. 254 71

A total of 13 phosphonate analogues of bis(5'-adenosyl) tetraphosphate (AppppA) have been tested as substrates and inhibitors of the asymmetrically cleaving bis(5'-nucleosidyl) tetraphosphatase (NppppNase) from Artemia and the symmetrically cleaving NppppNase from Escherichia coli. With the Artemia enzyme, the substrate efficiency of beta beta'-substituted compounds decreased with decreasing substituent electronegativity (O greater than CF2 greater than CHF greater than CCl2 greater than CHCl greater than CH2) such that AppCF2ppA and AppCH2ppA were hydrolyzed at 70% and 2.5% of the rate of AppppA, respectively. These compounds were competitive inhibitors of this enzyme with Ki values that generally also decreased with electronegativity from 12 microM for AppCF2ppA to 0.4 microM for AppCH2ppA (Km for AppppA = 33 microM). AppCH = CHppA and AppCH2CH2ppA were neither effective substrates nor inhibitors of the Artemia enzyme. Alpha beta,alpha'beta'-Disubstituted analogues were generally less effective inhibitors with Ki values ranging from 23 microM (ApCH2ppCH2pA) to greater than 1.5 mM (ApCH2CH2ppCH2CH2pA). However, they displayed a low and unexpected rate of symmetrical cleavage by the Artemia enzyme: e.g., ApCHFppCHFpA yielded ApCHFp at 3% of the rate of AppppA breakdown. Both sets of analogues were also competitive inhibitors of the E. coli NppppNase with Ki values ranging from 7 microM (AppCH2ppA) to 250 microM (ApCH2CH2ppCH2CH2pA) (Km for AppppA = 28 microM). The only alpha beta,alpha'beta'-disubstituted analogue to be hydrolyzed by the E. coli enzyme was ApCF2ppCF2pA at 0.2% of the rate of AppppA; however, several of the beta beta'-substituted compounds showed a limited degree of asymmetrical cleavage.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Recognition of beta beta'-substituted and alpha beta,alpha'beta'-disubstituted phosphonate analogues of bis(5'-adenosyl) tetraphosphate by the bis(5'-nucleosidyl)-tetraphosphate pyrophosphohydrolases from Artemia embryos and Escherichia coli. 254 83

Six new methylenephosphonate analogues of P1P4-bis-(5',5'''-adenosyl) tetraphosphate, Ap4A, having P2-P3 carbon bridges CF2, CCl2 and CH2CH2 or P1-P2 and P3-P4 carbon bridges CF2, CCl2 and CH2CH2 in the tetraphosphate chain, were examined as substrates or inhibitors for two specific Ap4A-degrading enzymes: (asymmetrical) Ap4A hydrolase (EC 3.6.1.17) from yellow-lupin seeds and (symmetrical) Ap4A hydrolase (EC 3.6.1.41) from Escherichia coli. All analogues in which the central oxygen atom was replaced by a stable carbon bridge were hydrolysed by the asymmetrical hydrolase (CF2 greater than CCl2 greater than O greater than CHBr greater than CH2 greater than CH2CH2). As expected, these analogues were not hydrolysed by the symmetrical hydrolase, which was also unable to act on analogues having P1-P2 and P3-P4 carbon bridges.
 ...
PMID:Studies on some specific Ap4A-degrading enzymes with the use of various methylene analogues of P1P4-bis-(5',5'''-adenosyl) tetraphosphate. 255 85

1. An enzyme has been isolated from Drosophila embryos which specifically hydrolyzes dinucleoside tetraphosphates to the corresponding nucleoside tri- and tetraphosphates, with Km values around 4 microM. 2. Nucleoside mono-, di- and triphosphates are competitive inhibitors with K1 values i the 0.01 mM range. 3. The inhibition is particularly strong by adenosine tetraphosphate (Ki = 10 nM). 4. The enzyme is maximally active at pH 7.5 and is quite stable at acid pH. 5. The enzyme requires divalent cations for activity: Co(2+) much greater than [corrected] Mn(2+) Mg(2+) x Co(2+) stimulated about 90-fold at 6 mM. 6. The specific stimulation by Co(2+) has been described before, but at lower concentrations, for the enzyme of procaryotes which splits diadenosine tetraphosphate symmetrically. Zn(2+) and Ca(2+) are inhibitors of the Drosophila enzyme. Co(2+) is also inhibitor in the presence of Mg(2+). 7. The Drosophila enzyme has essential sulphydryl group(s) and a molecular weight of 26,000. 8. Diadenosine tetraphosphatase is present in mature oocytes and increases after fertilization to reach a peak 1.5 hr later. 9. From this time to 3.5 hr the activity decreased to remain at a plateau until the end of embryogenesis. 10. The profile of activity is compatible with its involvement in the regulation of nuclear division.
 ...
PMID:Diadenosine 5",5"'P1,P4-tetraphosphatase in Drosophila embryos: developmental regulation and characterization. 255 22

Novel analogues of P1,P4-bis(5'-adenosyl) tetraphosphate, Ap4A (1), have been prepared with sulphur substituents at P1 and P4 and either oxygen or methylene bridges at the P2,P3-position. Separation of three isomers of the ApspCH2ppsA species has been achieved by a combination of mplc and hplc and the Rp,Rp, Rp,Sp, and Sp,Sp diastereoisomers identified on the basis of selective enzymatic hydrolysis using snake venom phosphodiesterase. Each of these three isomers is a strong competitive inhibitor of the specific Ap4Aase from Artemia and is highly resistant to the asymmetric cleavage normally catalysed by this enzyme.
 ...
PMID:Synthesis and resistance to enzymic hydrolysis of stereochemically-defined phosphonate and thiophosphate analogues of P1,P4-bis(5'-adenosyl) tetraphosphate. 282 89

Novel enzymatic activity which splits diadenosine 5',5'''-P1,P4-tetraphosphate (Ap4A) phosphorolytically has been found in extracts from Saccharomyces cerevisiae. One of the two alpha,beta-anhydride bonds between Ap4A phosphate residues undergoes phosphorolysis, and ATP (pppA) plus ADP (ppA) are the products of the reaction according to the equation: AppppA + P*i----pppA + p*pA The reaction is dependent on the presence of divalent metal ions; Mn2+ or Mg2+ sustain the greatest rates of reaction. Among analogues of the Ap4A substrate, Ap5A and Gp4G, but not p4A and Ap3A, are substrates, and corresponding products are p4A plus ADP, and GTP plus GDP, the phosphate being incorporated into the nucleoside 5'-diphosphates. In the reactions, phosphate can be substituted with arsenate. Arsenolysis of Ap4A, Ap5A, or Gp4G leads to ATP plus AMP, p4A plus AMP, and GTP plus GMP, respectively. The name diadenosine tetraphosphate alpha,beta-phosphorylase (ADP-forming) is proposed for the new enzyme. The phosphorylase has been purified to apparent homogeneity and behaves as a single polypeptide chain of Mr = 40,000. Optimum activity of the enzyme is at pH 8.0 and the sulfhydryl groups are essential for catalysis. At saturating Ap4A, the rate constant for the reaction is 36 s-1 and the Km value for Ap4A is 60 microM (37 degrees C, 50 mM Hepes/KOH (pH 8.2), 500 microM MnCl2, 10 mM K2HPO4, 1 mM 2-mercaptoethanol, and 2% glycerol). The Km values for phosphate and arsenate are 1 and 3 mM, respectively.
 ...
PMID:Phosphorolytic cleavage of diadenosine 5',5'''-P1,P4-tetraphosphate. Properties of homogeneous diadenosine 5',5'''-P1,P4-tetraphosphate alpha, beta-phosphorylase from Saccharomyces cerevisiae. 298 63

A clone overproducing diadenosine tetraphosphatase (diadenosine 5', 5'''-P1, P4-tetraphosphate pyrophosphohydrolase) activity was isolated from an Escherichia coli cosmid library. Localization of the DNA region responsible for stimulation of this activity was achieved by deletion mapping and subcloning in various vectors. Maxicell experiments and immunological assays demonstrated that a 3.5-kilobase-pair DNA fragment carried the structural gene apaH encoding the E. coli diadenosine tetraphosphatase. The DNA coding strand was determined by cloning this fragment in both orientations in pUC plasmids. It was also shown that the overproduction of diadenosine tetraphosphatase decreased the dinucleoside tetraphosphate concentration in E. coli by a factor of 10.
 ...
PMID:Molecular cloning of the Escherichia coli gene for diadenosine 5',5'''-P1,P4-tetraphosphate pyrophosphohydrolase. 299 25

DNA synthesis and adenosine(5')tetraphosphate(5')adenosine (Ap4A) levels decrease in cells treated with EDTA. The inhibitory effect of EDTA can be reversed with micromolar amounts of ZnCl2. ZnCl2 in micromolar concentrations also inhibits Ap4A hydrolase and stimulates amino acid-dependent Ap4A synthesis, suggesting that Zn2+ is modulating intracellular Ap4A pools. Serum addition to G1-arrested cells enhances uptake of Zn, whereas serum depletion leads to a fivefold decrease of the rates of zinc uptake. These results are discussed by regarding Zn2+ as a putative 'second messenger' of mitogenic induction and Ap4A as a possible 'third messenger' and trigger of DNA synthesis.
 ...
PMID:Zinc as a second messenger of mitogenic induction. Effects on diadenosine tetraphosphate (Ap4A) and DNA synthesis. 300 27

Complexation of putrescine, spermidine, spermine, and Mg2+ with diadenosine 5',5'''-P1,P4-tetraphosphate induces an upfield shift in the signals for the H-2 and H-8 protons. The upfield shifts in H-2 indicate that cation complexation enhances intramolecular adenine stacking interactions. The resonances for H-2 and H-8 of neutral analogs of 5',5'-dinucleotides appear farther upfield relative to the appropriate monomeric models than those for the corresponding dinucleotide; reduction of intra-chain phosphate repulsion is the origin of cation induced enhancement of diadenosine 5H,5'''-P1,P4-tetraphosphate base stacking.
 ...
PMID:A proton magnetic resonance study of the effects of polyamine and divalent metal ions on diadenosine 5',5'''-P1,P4-tetraphosphate base stacking. 303 69

An enzyme hydrolyzing diadenosine 5',5"'P1, P4-tetraphosphate (Ap4A) to AMP and ATP has been purified to apparent homogeneity from mouse liver cell extracts. The isolation procedure comprised ammonium sulfate precipitation, chromatography on Sephadex G-75. DEAE-cellulose, blue Sepharose and AMP-Sepharose. The enzyme is a single polypeptide chain with a native Mr = 64,000 with a Km of 1.66 microM and Vmax of 1.25 mumol/min. AMP, ADP, Ap4, GTP, Gp4, Ap3A, Ap5A, Gp3G, and Gp5G are noncompetitive inhibitors of the Ap4A hydrolase activity, whereas Gp4G inhibits Ap4A hydrolysis competitively with a Ki of 6 microM. Theophylline, caffeine, and isobutylmethylxanthine do not or only slightly inhibit Ap4A hydrolysis. Mitogenic factors have no effect on the enzymatic activity of Ap4A hydrolase, excluding that a direct influence of internalized mitogens on Ap4A degradation could be responsible for mitogen-dependent fluctuation of intracellular Ap4A pool sizes.
 ...
PMID:Diadenosine tetraphosphate hydrolase from mouse liver. Purification to homogeneity and partial characterization. 627 21


1 2 3 4 5 6 Next >>