An ATP-inhibited soluble 5'-nucleotidase of rat kidney

1988 ◽  
Vol 254 (2) ◽  
pp. F191-F195
Author(s):  
M. Le Hir ◽  
U. C. Dubach
Keyword(s):  
High Speed ◽  
Catalytic Properties ◽  
Divalent Cations ◽  
Rat Kidney ◽  
Maximal Activity ◽  
Rate Of Hydrolysis ◽  
Membrane Bound ◽  
Ph Range ◽  
Hydrolysis Of

Hydrolysis of 5'-AMP by 5'-nucleotidase is a possible source of adenosine in the kidney. A renal membrane-bound ecto-5'-nucleotidase has been previously described. The present study deals with the catalytic properties of a 5'-AMP phosphohydrolase partially purified from high-speed supernatants of rat kidney homogenates. It exhibits phosphatase activity toward 5'-AMP, 5'-IMP, and 5'-GMP, but not toward 2'- and 3'-AMP and corresponds therefore to a 5'-nucleotidase. The hydrolysis of 5'-AMP by the soluble 5'-nucleotidase requires divalent cations. Maximal activity is reached with 10 microM of either Mn2+ or Co2+, whereas half-maximal activity is obtained with approximately 400 microM Mg2+. The soluble 5'-nucleotidase exhibits Michaelis-Menten kinetics with a Km of 9.5 microM for 5'-AMP. In the presence of 1 mM of free Mg2+, physiological concentrations of ATP provoke an increase of the Km for 5'-AMP and a decrease of Vmax. An increase of the pH of 0.4 units in the pH range 6.4-7.4 roughly doubles the rate of hydrolysis of 5'-AMP. The effects of ATP and of the pH are compatible with a role of the renal soluble 5'-nucleotidase in the hydrolysis of 5'-AMP and in the production of adenosine during hypoxia.

Extracellular divalent cations in excitation–contraction coupling: hypertonic solution effects

1982 ◽  
Vol 60 (4) ◽  
pp. 440-445
Author(s):  
Isao Oota ◽  
Isao Kosaka ◽  
Torao Nagai ◽  
Hideyo Yabu
Keyword(s):  
Skeletal Muscle ◽  
Divalent Cations ◽  
Muscle Fibers ◽  
Hypertonic Solution ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling ◽  
Skeletal Muscle Fibers ◽  
Membrane Bound

It is the purpose of this article to point out that the membrane-bound Ca plays an important role in excitation–contraction (E–C) coupling of skeletal muscle fibers and that other divalent cations are unable to substitute for this role of membrane-bound Ca.

Functional role of ecto-ATPase activity in goldfish hepatocytes

1998 ◽  
Vol 274 (4) ◽  
pp. R1031-R1038 ◽  
Author(s):  
Pablo J. Schwarzbaum ◽  
Michael E. Frischmann ◽  
Gerhard Krumschnabel ◽  
Rolando C. Rossi ◽  
Wolfgang Wieser
Keyword(s):  
Atpase Activity ◽  
Functional Role ◽  
Maximal Activity ◽  
Hydrolysis Rate ◽  
Hyperbolic Function ◽  
Extracellular Release ◽  
Transport Atpases ◽  
Hydrolysis Of ◽  
Hepatocyte Suspension

Extracellular [γ-32P]ATP added to a suspension of goldfish hepatocytes can be hydrolyzed to ADP plus γ-32Pidue to the presence of an ecto-ATPase located in the plasma membrane. Ecto-ATPase activity was a hyperbolic function of ATP concentration ([ATP]), with apparent maximal activity of 8.3 ± 0.4 nmol Pi ⋅ (106cells)−1 ⋅ min−1and substrate concentration at which a half-maximal hydrolysis rate is obtained of 667 ± 123 μM. Ecto-ATPase activity was inhibited 70% by suramin but was insensitive to inhibitors of transport ATPases. Addition of 5 μM [α-32P]ATP to the hepatocyte suspension induced the extracellular release of α-32Pi[8.2 pmol ⋅ (106cells)−1 ⋅ min−1] and adenosine, suggesting the presence of other ectonucleotidase(s). Exposure of cell suspensions to 5 μM [2,8-3H]ATP resulted in uptake of [2,8-3H]adenosine at 7.9 pmol ⋅ (106cells)−1 ⋅ min−1. Addition of low micromolar [ATP] strongly increased cytosolic free Ca2+([Formula: see text]). This effect could be partially mimicked by adenosine 5′- O-(3-thiotriphosphate), a nonhydrolyzable analog of ATP. The blockage of both glycolysis and oxidative phosphorylation led to a sixfold increase of[Formula: see text] and an 80% decrease of intracellular ATP, but ecto-ATPase activity was insensitive to these metabolic changes. Ecto-ATPase activity represents the first step leading to the complete hydrolysis of extracellular ATP, which allows 1) termination of the action of ATP on specific purinoceptors and 2) the resulting adenosine to be taken up by the cells.

scholarly journals Kinetic studies on the acid hydrolysis of the methyl ketoside of unsubstituted and O-acetylated N-acetylneuraminic acid

1973 ◽  
Vol 133 (4) ◽  
pp. 623-628 ◽  
Author(s):  
A. Neuberger ◽  
Wendy A. Ratcliffe
Keyword(s):  
Sialic Acid ◽  
Acid Hydrolysis ◽  
Model Compound ◽  
Kinetic Studies ◽  
Order Rate Constant ◽  
Neuraminic Acid ◽  
Acetylneuraminic Acid ◽  
Rate Of Hydrolysis ◽  
Ph Range ◽  
Hydrolysis Of

The hydrolysis of the model compound 2-O-methyl-4,7,8,9-tetra-O-acetyl-N-acetyl-α-d-neuraminic acid and neuraminidase (Vibrio cholerae) closely resembled that of the O-acetylated sialic acid residues of rabbit Tamm–Horsfall glycoprotein. This confirmed that O-acetylation was responsible for the unusually slow rate of acid hydrolysis of O-acetylated sialic acid residues observed in rabbit Tamm–Horsfall glycoprotein and their resistance to hydrolysis by neuraminidase. The first-order rate constant of hydrolysis of 2-methyl-N-acetyl-α-d-neuraminic acid by 0.05m-H2SO4 was 56-fold greater than that of 2-O-methyl-4,7,8,9-tetra-O-acetyl-N-acetyl -α-d-neuraminic acid. Kinetic studies have shown that in the pH range 1.00–3.30, the observed rate of hydrolysis of 2-methyl-N-acetyl-α-d-neuraminic acid can be attributed to acid-catalysed hydrolysis of the negatively charged CO2− form of the methyl ketoside.

A Study on the Effect of Lysolecithin and Phospholipase A on Membrane-Bound Galactosyltransferase

1974 ◽  
Vol 52 (11) ◽  
pp. 1053-1066 ◽  
Author(s):  
Sailen Mookerjea ◽  
James W. M. Yung
Keyword(s):  
Liver Microsomes ◽  
Fatty Acyl ◽  
Phospholipase A ◽  
Synthetase Activity ◽  
Rat Liver Microsomes ◽  
Physiological Concentration ◽  
Activation Effect ◽  
Membrane Bound ◽  
Hydrolysis Of

Addition of lysolecithin caused very marked activation of UDP-galactose:glycoprotein galactosyltransferase in rat liver microsomes and in Golgi-rich membranes. Lysolecithin activated galactosyltransferase when the enzyme was assayed both with endogenous acceptor and with exogenous proteins or monosaccharides as acceptors. Lactose synthetase activity in presence of α-lactalbumin was also stimulated by lysolecithin. Lecithin, lysophosphatidylethanolamine, lysophosphatidic acid, and glycerophosphorylcholine did not activate the enzyme, suggesting that both fatty acyl and phosphorylcholine groups of the lysolecithin molecule are required for the observed activation. The degree of activation was about the same when myristoyl-, palmitoyl-, oleoyl-, or stearoyllysolecithin were tested. The activation by lysolecithin was observed well within the physiological concentration of the lipid in the liver cell. Saturating amounts of Triton masked the effect of lysolecithin.Brief preincubation with phospholipase A activated the enzyme and generated lysolecithin in the membranes. Triton and lysolecithin activated the enzyme without any lag time, whereas phospholipase A activation was dependent on preincubation and also on an alkaline pH favorable for the hydrolysis of phospholipid. EDTA blocked the activation effect of phospholipase A but had no effect on activation by lysolecithin. Albumin and cholesterol opposed the effects of lysolecithin and phospholipase A on the enzyme. Two successive incubations of the microsomes with lysolecithin caused considerable release of the enzyme into the soluble fraction. The role of lysolecithin in the activation of the enzyme is probably related to the solubilization of the membrane and consequent enhanced interaction of the enzyme with substrate. Lysolecithin also activated N-acetylglucosaminyl- and sialyltransferase activities in microsomes. A possible role of lysolecithin is indicated in the regulation of glycosylation reactions in mammalian system.

Role of the Sarcoplasmic Reticulum Ca2+-ATPase on Heat Production and Thermogenesis

2001 ◽  
Vol 21 (2) ◽  
pp. 113-137 ◽  
Author(s):  
Leopoldo de Meis
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Atp Hydrolysis ◽  
Surrounding Medium ◽  
Chemical Energy ◽  
The Past ◽  
Sarcoplasmic Reticulum Membrane ◽  
Membrane Bound ◽  
Hydrolysis Of ◽  
Heat Released

The sarcoplasmic reticulum of skeletal muscle retains a membrane bound Ca2+-ATPase which is able to interconvert different forms of energy. A part of the chemical energy released during ATP hydrolysis is converted into heat and in the bibliography it is assumed that the amount of heat produced during the hydrolysis of an ATP molecule is always the same, as if the energy released during ATP cleavage were divided in two non-interchangeable parts: one would be converted into heat, and the other used for Ca2+ transport. Data obtained in our laboratory during the past three years indicate that the amount of heat released during the hydrolysis of ATP may vary between 7 and 32 kcal/mol depending on whether or not a transmembrane Ca2+ gradient is formed across the sarcoplasmic reticulum membrane. Drugs such as heparin and dimethyl sulfoxide are able to modify the fraction of the chemical energy released during ATP hydrolysis which is used for Ca2+ transport and the fraction which is dissipated in the surrounding medium as heat.

Role of trinuclear Zn(II) complexes in promoting the hydrolysis of 4-nitrophenyl acetate

2004 ◽  
Vol 82 (3) ◽  
pp. 409-417 ◽  
Author(s):  
Qing-Chun Ge ◽  
Yan-He Guo ◽  
Hai Lin ◽  
Dong-Zhao Gao ◽  
Hua-Kuan Lin ◽  
...  
Keyword(s):  
Rate Constants ◽  
Volume Fraction ◽  
Bound Water ◽  
Catalytic Efficiency ◽  
Active Species ◽  
Nucleophilic Attack ◽  
Carboxyl Oxygen Atom ◽  
Ph Range ◽  
Hydrolysis Of

Potentiometric determination shows that trinuclear Zn(II) complexes of the four tripods 1,3,5-tri(2′,5′-diazahexyl)benzene (L1), 1,3,5-tri(2′,5′-diazaheptyl)benzene (L2), 1,3,5-tri(2′,5′-diazaoctyl)benzene (L3), and 1,3,5-tri(2′,5′-diazanonyl)benzene (L4) could be potential hydrolytic catalysts. CH3CN solutions containing [3Zn:L]T (0.5~2 × 10–3 mol·dm–3) with I = 0.10 mol·dm–3 of KNO3 and Good's buffer (10% volume fraction) were studied for the catalyzing hydrolysis of p-nitrophenyl acetate (NA, 0.5~2 × 10–3 mol·dm–3), at 298 K, in the 6.5–8.2 pH range. The observed rate constants, kobs, fit the equilibrium equation kobs = kcom [3Zn:L]T + kOH[OH–] + k0. The sigmoid pH~kcom profiles for NA hydrolysis suggest that either the Zn(II)-bound hydroxyl or the Zn(II)-bound water forms of the catalysts can be the active species. The observed second-order rate constants are 0.0082, 0.011, 0.0059, and 0.0019 mol–1·dm3·s–1 for the four Zn3L–H2O complexes (kA) and 0.342, 0.257, 0.382, and 0.091 mol–1·dm3·s–1 for the four Zn3L–OH- groups (kB), respectively. However, under the condition that [NA] = 0.5 × 10–3 mol·dm–3 and [3Zn:L1]T = 2~4 × 10–2 mol·dm–3 at pH 7.6, the observed rate constants, kobs, obey the equilibrium kobs = kcom[3Zn:L]T/(1/K′ + [3Zn:L]T). This indicates that the 3:1 complex (or its deprotonated hydroxide form) mediates NA hydrolysis by nucleophilic attack of the carboxyl center with the pre-formation of a coordination bond between the carboxyl oxygen atom and the Zn(II) ion. Comparison with other models was made, and the reasons for the high catalytic efficiency of the tripodal complexes were given.Key words: tripod, Zn(II), catalysis, NA hydrolysis, polynuclear.

scholarly journals Functionalized Oxoindolin Hydrazine Carbothioamide Derivatives as Highly Potent Inhibitors of Nucleoside Triphosphate Diphosphohydrolases

2020 ◽  
Vol 11 ◽  
Author(s):  
Saira Afzal ◽  
Mariya al-Rashida ◽  
Abdul Hameed ◽  
Julie Pelletier ◽  
Jean Sévigny ◽  
...  
Keyword(s):  
Gene Expression ◽  
Insulin Secretion ◽  
Molecular Docking ◽  
Docking Studies ◽  
Nucleoside Triphosphate ◽  
Membrane Bound ◽  
Hydrolysis Of ◽  
Extracellular Environment ◽  
Micromolar Range

Ectonucleoside triphosphate diphosphohydrolases (NTPDases) are ectoenzymes that play an important role in the hydrolysis of nucleoside triphosphate and diphosphate to nucleoside monophosphate. NTPDase1, -2, -3 and -8 are the membrane bound members of this enzyme family that are responsible for regulating the levels of nucleotides in extracellular environment. However, the pathophysiological functions of these enzymes are not fully understood due to lack of potent and selective NTPDase inhibitors. Herein, a series of oxoindolin hydrazine carbothioamide derivatives is synthesized and screened for NTPDase inhibitory activity. Four compounds were identified as selective inhibitors of h-NTPDase1 having IC50 values in lower micromolar range, these include compounds 8b (IC50 = 0.29 ± 0.02 µM), 8e (IC50 = 0.15 ± 0.009 µM), 8f (IC50 = 0.24 ± 0.01 µM) and 8l (IC50 = 0.30 ± 0.03 µM). Similarly, compound 8k (IC50 = 0.16 ± 0.01 µM) was found to be a selective h-NTPDase2 inhibitor. In case of h-NTPDase3, most potent inhibitors were compounds 8c (IC50 = 0.19 ± 0.02 µM) and 8m (IC50 = 0.38 ± 0.03 µM). Since NTPDase3 has been reported to be associated with the regulation of insulin secretion, we evaluated our synthesized NTPDase3 inhibitors for their ability to stimulate insulin secretion in isolated mice islets. Promising results were obtained showing that compound 8m potently stimulated insulin secretion without affecting the NTPDase3 gene expression. Molecular docking studies of the most potent compounds were also carried out to rationalize binding site interactions. Hence, these compounds are useful tools to study the role of NTPDase3 in insulin secretion.

THE HYDROLYSIS OF THE CONDENSED PHOSPHATES: III. SODIUM TETRAMETAPHOSPHATE AND SODIUM TETRAPHOSPHATE

1956 ◽  
Vol 34 (7) ◽  
pp. 969-981 ◽  
Author(s):  
Joan Crowther ◽  
A. E. R. Westman
Keyword(s):  
Phosphate Glass ◽  
Sodium Phosphate ◽  
Hydrogen Ion ◽  
Ion Concentrations ◽  
First Order ◽  
Condensed Phosphates ◽  
Rate Of Hydrolysis ◽  
Acid Catalyzed ◽  
Ph Range ◽  
Hydrolysis Of

The rates of hydrolysis of sodium tetrametaphosphate and tetraphosphate (in the presence of tetrametaphosphate) have been measured at 65.5 °C. over the pH range 2.5 to 13.3. Tetrametaphosphate anions hydrolyze to tetraphosphate which in turn hydrolyzes to triphosphate and orthophosphate and not to pyrophosphate. Thus the terminal oxygen bridges in the tetraphosphate and not the central one are attacked preferentially. The reactions were first order and acid catalyzed. The tetrametaphosphate hydrolysis was also base catalyzed with a minimum rate in solutions of pH approximately 7.5. The rate of hydrolysis of tetraphosphate was greater than triphosphate at the hydrogen ion concentrations studied. Hydrolysis of a sodium phosphate glass indicated that preferential attack on terminal oxygen bridges takes place also with higher polymers. However, trimetaphosphate is formed at the same time.

scholarly journals Bacillus macyae sp. nov., an arsenate-respiring bacterium isolated from an Australian gold mine

2004 ◽  
Vol 54 (6) ◽  
pp. 2241-2244 ◽  
Author(s):  
Joanne M. Santini ◽  
Illo C. A. Streimann ◽  
Rachel N. vanden Hoven
Keyword(s):  
Dna Hybridization ◽  
Gene Sequence ◽  
Maximal Activity ◽  
Rrna Gene ◽  
Strictly Anaerobic ◽  
Gold Mine ◽  
Terminal Electron Acceptor ◽  
Gene Sequence Analysis ◽  
Membrane Bound ◽  
Ph Range

A strictly anaerobic arsenate-respiring bacterium isolated from a gold mine in Bendigo, Victoria, Australia, belonging to the genus Bacillus is described. Cells are Gram-positive, motile rods capable of respiring with arsenate and nitrate as terminal electron acceptors using a variety of substrates, including acetate as the electron donor. Reduction of arsenate to arsenite is catalysed by a membrane-bound arsenate reductase that displays activity over a broad pH range. Synthesis of the enzyme is regulated; maximal activity is obtained when the organism is grown with arsenate as the terminal electron acceptor and no activity is detectable when it is grown with nitrate. Mass of the catalytic subunit was determined to be approximately 87 kDa based on ingel activity stains. The closest phylogenetic relative, based on 16S rRNA gene sequence analysis, is Bacillus arseniciselenatis, but DNA–DNA hybridization experiments clearly show that strain JMM-4T represents a novel Bacillus species, for which the name Bacillus macyae sp. nov. is proposed. The type strain is JMM-4T (=DSM 16346T=JCM 12340T).

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