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Results for “Pyrophosphatases”

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PubMed1986

ATP sulfurylase-dependent assays for inorganic pyrophosphate: applications to determining the equilibrium constant and reverse direction kinetics of the pyrophosphatase reaction, magnesium binding to orthophosphate, and unknown concentrations of pyrophosphate.

A continuous, coupled, spectrophotometric assay is described in which the enzyme ATP sulfurylase is employed to measure the concentration of inorganic pyrophosphate (PPi) at equilibrium with known concentrations of inorganic orthophosphate (Pi) in the presence of excess inorganic pyrophosphatase (PPitase). In agreement with previous reports, the apparent equilibrium constant (Keq,app) of the PPi hydrolysis reaction was shown to decrease as the concentration of Mg2+ is increased. At pH 7.3, 30 degrees C, in the presence of 150 mM NaCl and 1 mM free Mg2+, Keq,app (calculated as [Pi]t2/[PPi]t) was 1950. Measurements of Keq,app at different total concentrations of Mg2+ and Pi permitted the determination of K0, the dissociation constant of the Mg-Pi complex. In 0.05 M Tris-Cl, pH 8.0, at 30 degrees C, K0 was 3.6 mM. In the presence of excess ATP sulfurylase, yeast PPitase catalyzed PPi formation from Pi with a specific activity (Vmax) of 9 units X mg protein-1 at pH 8.0, 30 degrees C, and 1 mM free Mg2+. Half-maximum reverse reaction velocity was observed at a total Pi concentration of 18 mM. (Under the same conditions, Vmax of the PPi hydrolysis reaction was 530 units X mg protein-1.) A radiochemical end point ("reaction-to-completion") assay for measuring unknown concentrations of PPi was devised. In the presence of excess 35S-adenosine-5'-phosphosulfate ([35S]APS) as the cosubstrate, 35SO2-4 formation was stoichiometric with added PPi. (The 35SO2-4 and [35S]APS are separated by adsorption of the latter onto charcoal.) The sensitivity of the assay can be adjusted by varying the specific radioactivity of the [35S]APS. In the absence of interfering substances, as little as 2 pmol of PPi per 1.0 ml assay volume can be measured. The sensitivity of the assay is reduced in the presence of ATP plus perchlorate (which synergistically inhibit the enzyme). However, if the bulk of the ATP is removed from perchloric acid extracts of tissues with glucose and hexokinase, initial intracellular levels as low as 1 microM can be measured. The possibility that most of the cellular PPi extracted with perchloric acid was originally enzyme bound is discussed.

Diphosphates↗

PubMed1985

The phosphate-pyrophosphate exchange and hydrolytic reactions of the membrane-bound pyrophosphatase of Rhodospirillum rubrum: effects of Mg2+, phosphate, and pyrophosphate.

The relation that exists between the Pi-PPi exchange reaction and pyrophosphate hydrolysis by the membrane-bound pyrophosphatase of chromatophores of Rhodospirillum rubrum was studied. The two reactions have a markedly different requirement for added Mg2+. Optimal rates of hydrolysis were attained at 1 mM Mg2+ with 0.67 mM pyrophosphate; the rate od hydrolysis correlated with the concentration of Mg-pyrophosphate, which indicated that the latter was the substrate for hydrolysis. The Pi-PPi exchange reaction rate was low at concentrations of added Mg2+ below 1 mM (0.67 mM pyrophosphate), but increased as the concentration of Mg2+ in the medium was increased. The Pi-PPi exchange reaction depends on the concentration of MgHPO4, which suggests that this is the substrate in the exchange reaction. However, it is likely that free Mg2+ also exerts a favorable effect on the Pi-PPi exchange reaction. The optimal concentration for the Pi-PPI exchange reaction was approx 240 microM, which suggests that the concentration of the hydrolyzable substrates modulates the kinetic characteristics of the enzyme.

Cell Membrane↗

PubMed1988

Properties and regulation of Mg2+-dependent chloroplast inorganic pyrophosphatase from Sorghum vulgare leaves.

A Mg2+ dependent inorganic pyrophosphatase from chloroplasts of Sorghum vulgare has been purified 275-fold to electrophoretic purity with an overall recovery of about 25% activity. Estimations of native and monomeric relative molecular weights by size exclusion chromatography and denaturing electrophoresis suggest that the holoenzyme is a monomer of 42 +/- 1.5 kDa. A high specificity for tetrasodium pyrophosphate (PPi) as substrate has been observed, as the other phosphoesters tested were virtually unaffected. The Mg2+:PPi ratio of 5:1 at pH 8.0 shifts to 2.5:1.0 at pH 9.0 and 10:1 at pH 7.0. None of the divalent cations tested could substitute for Mg2+. Further, in the presence of Mg2+, these divalent cations inhibit the catalytic hydrolysis of PPi. EDTA rapidly and irreversibly inactivates the purified enzyme in a biphasic manner. Of the metabolites tested, Pi and L-malate significantly inhibited the catalytic activity of the enzyme. Malate inhibits the enzyme through an allosteric mechanism. A Hill plot of this inhibition shows that at least two molecules of malate bind to each molecule of the purified enzyme. The likely physiological significance of this result is discussed.

Cations, Divalent↗

PubMed1989

Allosteric regulation of yeast inorganic pyrophosphatase by substrate.

Kinetic and binding studies of yeast inorganic pyrophosphatase (EC 3.6.1.1) revealed a regulatory PPi-binding site. Rate vs substrate concentration dependencies were markedly nonhyperbolic in the range of 0.1-150 microM MgPPi at fixed Mg2+ levels of 0.05-10 mM provided that the enzyme had been preequilibrated with Mg2+. Imidodiphosphate, hydroxymethylenebisphosphonate, and phosphate eliminated the deviations from the Michaelis-Menten kinetics and inhibited PPi hydrolysis in a manner consistent with their binding at both active and regulatory sites. The results agreed with a model in which binding of uncomplexed PPi at the regulatory site markedly increases enzyme affinity for the activating Mg2+ ion. Ultrafiltration studies revealed the binding of at least 3 mol of the inhibitory hydroxymethylenebisphosphonate and of 2 mol of noninhibitory methylenebisphosphonate per mole of the dimeric enzyme.

Allosteric Regulation↗

PubMed1992

Molecular cloning of cDNAs for human fibroblast nucleotide pyrophosphatase.

Nucleotide pyrophosphatase (NPPase) activity is markedly elevated in cultured skin fibroblasts from patients of Lowe's syndrome. cDNA clones encoding the NPPase were isolated using synthetic oligonucleotide probes designed on the basis of partial amino acid sequence of the enzyme purified from human placenta. The complete sequences of these clones yielded a merged sequence of 3508 bases. The polypeptide chain of the enzyme was deduced to comprise 873 amino acids with a calculated molecular weight of 99,703 and had the characteristics of a class II transmembrane protein. Ten potential N-glycosylation sites were detected in the protein. RNA blot analysis showed that human fibroblasts contain two minor mRNAs of 7.0 and 8.2 kb, respectively, in addition to a major 3.6-kb species that coincides with the merged cDNA in size. A computer search of a nucleotide sequence data-base revealed that plasma cell membrane glycoprotein PC-1, whose function was unknown at the time, is identical with the NPPase. Comparison of the amino acid sequence of the NPPase with the active site sequence of bovine 5'-nucleotide phosphodiesterase allowed the assignment of a putative active site domain to the central region of the COOH-terminal extracellular domain of the NPPase. The gene for human NPPase was localized to chromosome 6 at q22-q23 by in situ hybridization with a fragment of the NPPase cDNA.

Amino Acid Sequence↗

PubMed1989

The effects of cadmium on the p-nitrophenyl phosphatase and inorganic pyrophosphatase activities of alkaline phosphatase in developing hamster tooth germs.

p-Nitrophenyl phosphatase (p-NPP-ase) and inorganic pyrophosphatase (PPi-ase) activities originate from the same alkaline phosphatase enzyme. Only the PPi-ase site has zinc (Zn2+) as a cofactor. Cadmium (Cd2+) in concentrations from 10(-5) mol/l upwards inhibited the PPi-ase activity, but did not inhibit the p-NPP-ase activity at all. In mineralizing tooth germs Cd2+ may replace Zn2+, thereby changing the specific stereoconfiguration in the active centre needed for PPi-ase activity, but not that for p-NPP-ase activity.

4-Nitrophenylphosphatase↗

PubMed1991

A vacuolar ATPase and pyrophosphatase in Acetabularia acetabulum.

Vacuole-rich fractions were isolated from Acetabularia acetabulum by Ficoll step gradient centrifugation. The tonoplast-rich vesicles showed ATP-dependent and pyrophosphate-dependent H(+)-transport activities. ATP-dependent H(+)-transport and ATPase activity were both inhibited by the addition of a specific inhibitor of vacuolar ATPase, bafilomycin B1. A 66 kDa polypeptide present in the preparation cross-reacted with the anti-IgG fractions against the alpha and beta subunits of Halobacterium halobium ATPase and with the antibody against the A subunit (68 kDa subunit) of mung bean vacuolar ATPase. A 56 kDa polypeptide present in the vacuole preparation showed cross-reactivity with the antibody against the B subunit (57 kDa) of mung bean vacuolar ATPase but not with the anti-beta subunit of H. halobium ATPase. A 73 kDa polypeptide cross-reacted with the antibody against inorganic pyrophosphatase of mung bean vacuoles. These results suggest that vacuolar membrane of A. acetabulum equipped energy transducing systems similar to those found in other plant vacuoles.

Acetabularia↗

PubMed1979

Fluoride inhibition of inorganic pyrophosphatase. IV. Evidence for metal participation in the active center and a four-site model of metal effect on catalysis.

Atomic spectroscopy of native yeast inorganic pyrophosphatase (pyrophosphate phosphohydrolase, EC 3.6.1.1) after gel filtration showed that it only binds activating Mg2% in an easily dissociable manner. Formation of a covalent intermediate between the enzyme and an entire substrate molecular in the presence of fluoride, however, dramatically strengthened the binding of two Mg2+ per subunit and eliminated at neutral pH the effect of added metals on protein fluorescence but not on the absorption spectrum, suggesting that different mental binding sites influence the two spectra. This conclusion was confirmed by spectra studied on native enzyme. A third, low-affinity site for Mg2+ was found on the enzyme pH greater than 8. A model of enzyme-substrate-metal interactions was proposed, according to which the fluorescence-controlling site belongs to the active center and substrate can only be bound to it as a 1 : 1 complex with metals.

Binding Sites↗

PubMed1990

Purification and characterization of two proteins with inorganic pyrophosphatase activity from Desulfovibrio vulgaris: rubrerythrin and a new, highly active, enzyme.

The inorganic pyrophosphatase activity of a soluble extract from the strict anaerobe, sulfate-reducing, Desulfovibrio vulgaris, is readily resolved into two peaks. After purification, two active proteins with very dissimilar properties are obtained. One is the non-heme iron-containing rubrerythrin, with a specific activity of 350 pyrophosphate hydrolyzed, min-1, mg protein-1. The other, a protein of Mr = 39,000, with a specific activity of 12,000.

Amino Acid Sequence↗

PubMed1988

Elevated nucleotide pyrophosphatase activity in cultured skin fibroblasts from patients with Lowe's syndrome.

In previous papers we reported that nucleotide pyrophosphatase (NPPase) activities are markedly elevated in skin fibroblasts from patients with Lowe's syndrome. To reveal the molecular basis for this elevation, we investigated to see whether or not the activities are proportional to the amounts of enzyme protein. Determination of the amounts of NPPase proteins by a radioimmunoassay using monoclonal antibodies revealed that the amounts of NPPase proteins were proportional to the enzyme activities. The NPPase proteins from patients' and normal cells were indistinguishable, after SDS-polyacrylamide gel electrophoresis, on Western blot analysis with staining with polyclonal antibodies raised against denatured NPPase. These data suggested that the elevated NPPase activities in fibroblasts in this disorder resulted from increased amounts of the enzyme proteins.

Antibodies, Monoclonal↗

PubMed1989

A specific, low Km ADP-ribose pyrophosphatase from rat liver.

Two rat liver ADP-ribose pyrophosphatases (ADPRibases) were partially purified. ADPRibase-I hydrolyzed ADP-ribose (Km = 0.5 microM) giving AMP as a product, required Mg2+ or, less efficiently, Mn2+ (Ca2+ was not active), its activity changed little between pH 7 and 9, and was specific for ADP-ribose as it did not hydrolyze ADP-glucose, NAD+, NADH or diadenosine 5',5"'-P1,Pn-n-phosphates (Ap2A, Ap3A). ADPRibase-II showed similar properties, except that the Km for ADP-ribose was 50 microM and may be non-specific, as the same preparation hydrolyzed ADP-glucose, NADH and Ap2A. ADPRibase-I fulfills the requirements of a specific turnover pathway consistent with a cellular role for free ADP-ribose.

Adenosine Diphosphate Glucose↗

PubMed1990

Tightly bound pyrophosphate in Escherichia coli inorganic pyrophosphatase.

Hexameric inorganic pyrophosphatase of Escherichia coli contains about 1 mol/mol of 'structural' pyrophosphate, which survives gel filtration and prolonged incubation with Mg2+, does not exchange with medium phosphate and pyrophosphate but is removed with 0.8 M perchloric acid. The site of pyrophosphate binding seems to be another than the active site. An additional 0.9 mol of enzyme-bound pyrophosphate is formed in the presence of phosphate and Mg2+ but this pyrophosphate is in fast equilibrium with medium phosphate and appears to be bound to the active site.

Animals↗

PubMed1991

Dimeric structure of H(+)-translocating pyrophosphatase from pumpkin vacuolar membranes.

Vacuolar membrane H(+)-translocating pyrophosphatase (H(+)-PPase) was purified from pumpkin seedlings. Its enzymatic properties including molecular size of constituting polypeptide (75 kDa) were very similar to those of mung bean H(+)-PPase [(1989) J. Biol. Chem. 264, 20068-20073]. The native, functional molecular size of the pumpkin H(+)-PPase was estimated to be 135-139 kDa from gel permeation HPLC of the purified enzyme in the presence of detergent and from radiation inactivation of the enzyme in vacuolar membranes. It is concluded that native, functional pumpkin H(+)-PPase, and also probably H(+)-PPases from other plants, is a dimer of 75 kDa subunits.

Biological Transport, Active↗

PubMed1994

Oxygen exchange reactions catalyzed by vacuolar H(+)-translocating pyrophosphatase. Evidence for reversible formation of enzyme-bound pyrophosphate.

Vacuolar membrane-derived vesicles isolated from Vigna radiata catalyze oxygen exchange between medium phosphate and water. On the basis of the inhibitor sensitivity and cation requirements of the exchange activity, it is almost exclusively attributable to the vacuolar H(+)-pyrophosphatase (V-PPase). The invariance of the partition coefficient and the results of kinetic modeling indicate that exchange proceeds via a single reaction pathway and results from the reversal of enzyme-bound pyrophosphate synthesis. Comparison of the exchange reactions catalyzed by V-PPase and soluble PPases suggests that the two classes of enzyme mediate P(i)-HOH exchange by the same mechanism and that the intrinsic reversibility of the V-PPase is no greater than that of soluble PPases.

Diphosphates↗

PubMed1995

Cold lability of the mutant forms of Escherichia coli inorganic pyrophosphatase.

The variants of Escherichia coli pyrophosphatase carrying the substitutions Glu20-->Asp, His136-->Gln or His140-->Gln are inactivated, in contrast to the wild-type enzyme, at temperatures below 25 degrees C: their activity measured at 25 degrees C decreases with decreasing the temperature of the stock enzyme solution. The inactivation is completely reversible and is explained by cold-induced dissociation of these hexameric enzymes into less active trimers.

Aspartic Acid↗

PubMed1992

dUTP pyrophosphatase and uracil-DNA glycosylase in rat liver and hepatomas.

1. The activity of dUTP pyrophosphatase (dUTPase) was similar in rat liver and hepatomas of slow or moderate growth rate but was increased several fold in three rapidly growing hepatomas. 2. There was an approx three-fold increase in the activity of uracil-DNA glycosylase in Morris hepatoma 7800 but there was little change in activity in other hepatomas that were examined. 3. The activities of dUTPase and uracil-DNA glycosylase were not significantly affected by two diets that may be promotional for hepatocarcinogenesis, a high orotate diet and an arginine-deficient diet.

Animals↗

PubMed1993

Modification of tryptophan 149 of inorganic pyrophosphatase from Escherichia coli.

1. The inorganic pyrophosphatase from Escherichia coli was almost completely inactivated on chemical modification of Trp-149 with N-bromosuccinimide (NBS). 2. The presence of a complex of Mg2+ and a substrate analogue, iminodiphosphate (PNP), provided considerable protection against the inactivation, whereas Mg2+ or PNP alone afforded only slight protection.

Amino Acid Sequence↗

PubMed1992

Thiamin mono- and pyrophosphatase activities from brain homogenate of Guamanian amyotrophic lateral sclerosis and parkinsonism-dementia patients.

Thiamin-pyrophosphatase (TPPase) and thiamin-monophosphatase (TMPase) were determined using a spectrophotometric method at various pH values (5.5, 7.5, and 9.0) in brain tissue obtained at autopsy from amyotrophic lateral sclerosis (ALS) and parkinsonism-dementia (PD) patients from Guam and from Guamanian patients who died from other diseases (controls). TPPase separation by thin-layer polyacrylamide gel isoelectric focusing (IEF) was also performed using both gray and white matter. TPPase content, chemically determined at pH 9.0, was found to be significantly reduced in the frontal cortex of ALS and PD patients compared to controls. TMPase content, on the contrary, was unchanged. IEF analysis showed 9 clear-cut bands with TPPase activity in the pH range 5.4-7.2 and a broad band at pH 4.7-5.2. The enzymatic activity was higher in gray than in white matter. In one patient the pattern was clearly different, with two additional bands observed at pH 7.1 and 6.7, and thought to be due to genetic microheterogeneity.

Aged↗