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Purification and characterization of pyrophosphate- and ATP-dependent phosphofructokinases from banana fruit.

Pyrophosphate-dependent phosphofructokinase (PFP; EC 2.7.1.90) and two isoforms of ATP-dependent phosphofructokinase (PFK I and PFK II; EC 2.7.1.11) from ripened banana ( Musa cavendishii L. cv. Cavendish) fruits were resolved via hydrophobic interaction fast protein liquid chromatography (FPLC), and further purified using anion-exchange and gel filtration FPLC. PFP was purified 1,158-fold to a final specific activity of 13.9 micromol fructose 1,6-bisphosphate produced (mg protein)(-1) x min(-1). Gel filtration FPLC and immunoblot analyses indicated that this PFP exists as a 490-kDa heterooctomer composed of equal amounts of 66- (alpha) and 60-kDa (beta) subunits. PFP displayed hyperbolic saturation kinetics for fructose 6-phosphate (Fru 6-P), PPi, fructose 1,6-bisphosphate, and Pi ( K(m) values = 32, 9.7, 25, and 410 microM, respectively) in the presence of saturating (5 microM) fructose 2,6-bisphosphate, which elicited a 24-fold enhancement of glycolytic PFP activity ( K(a)=8 nM). PFK I and PFK II were each purified about 350-fold to final specific activities of 5.5-6.0 micromol fructose 1,6-bisphosphate produced (mg protein)(-1) x min(-1). Analytical gel filtration yielded respective native molecular masses of 210 and 160 kDa for PFK I and PFK II. Several properties of PFK I and PFK II were consistent with their respective designation as plastid and cytosolic PFK isozymes. PFK I and PFK II exhibited: (i) pH optima of 8.0 and 7.3, respectively; (ii) hyperbolic saturation kinetics for ATP ( K(m)=34 and 21 microM, respectively); and (iii) sigmoidal saturation kinetics for Fru 6-P ( S0.5=540 and 90 microM, respectively). Allosteric effects of phospho enolpyruvate (PEP) and Pi on the activities of PFP, PFK I, and PFK II were characterized. Increasing concentrations of PEP or Pi progressively disrupted fructose 2,6-bisphosphate binding by PFP. PEP potently inhibited PFK I and to a lesser extent PFK II ( I50=2.3 and 900 microM, respectively), while Pi activated PFK I by reducing its sensitivity to PEP inhibition. Our results are consistent with: (i) the respiratory climacteric being regulated by fine (allosteric) control of pre-existing enzymes; and (ii) primary and secondary glycolytic flux control being exerted at the levels of PEP and Fru 6-P metabolism, respectively.

Adenosine Triphosphate↗

Induction of a leaf specific geranylgeranyl pyrophosphate synthase and emission of (E,E)-4,8,12-trimethyltrideca-1,3,7,11-tetraene in tomato are dependent on both jasmonic acid and salicylic acid signaling pathways.

Two cDNAs encoding geranylgeranyl pyrophosphate (GGPP) synthases from tomato (Lycopersicon esculentum) have been cloned and functionally expressed in Escherichia coli. LeGGPS1 was predominantly expressed in leaf tissue and LeGGPS2 in ripening fruit and flower tissue. LeGGPS1 expression was induced in leaves by spider mite (Tetranychus urticae)-feeding and mechanical wounding in wild type tomato but not in the jasmonic acid (JA)-response mutant def-1 and the salicylic acid (SA)-deficient transgenic NahG line. Furthermore, LeGGPS1 expression could be induced in leaves of wild type tomato plants by JA- or methyl salicylate (MeSA)-treatment. In contrast, expression of LeGGPS2 was not induced in leaves by spider mite-feeding, wounding, JA- or MeSA-treatment. We show that emission of the GGPP-derived volatile terpenoid (E,E)-4,8,12-trimethyltrideca-1,3,7,11-tetraene (TMTT) correlates with expression of LeGGPS1. An exception was MeSA-treatment, which resulted in induction of LeGGPS1 but not in emission of TMTT. We show that there is an additional layer of regulation, because geranyllinalool synthase, catalyzing the first dedicated step in TMTT biosynthesis, was induced by JA but not by MeSA.

Acyclic Monoterpenes↗

Fructose 2,6-bisphosphate activates pyrophosphate: fructose-6-phosphate 1-phosphotransferase and increases triose phosphate to hexose phosphate cycling in heterotrophic cells.

The aim of this work was to establish the influence of fructose 2,6-bisphosphate (Fru-2,6-P2) on non-photosynthetic carbohydrate metabolism in plants. Heterotrophic callus lines exhibiting elevated levels of Fru-2,6-P2 were generated from transgenic tobacco (Nicotiana tabacum L.) plants expressing a modified rat liver 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase. Lines containing increased amounts of Fru-2,6-P2 had lower levels of hexose phosphates and higher levels of 3-phosphoglycerate than the untransformed control cultures. There was also a greater redistribution of label into the C6 position of sucrose and fructose, following incubation with [1-13C]glucose, in the lines possessing the highest amounts of Fru-2,6-P2, indicating a greater re-synthesis of hexose phosphates from triose phosphates in these lines. Despite these changes, there were no marked differences between lines in the metabolism of 14C-substrates, the rate of oxygen uptake, carbohydrate accumulation or nucleotide pool sizes. These data provide direct evidence that physiologically relevant changes in the level of Fru-2,6-P2 can affect pyrophosphate: fructose-6-phosphate 1-phosphotransferase (PFP) activity in vivo, and are consistent with PFP operating in a net glycolytic direction in the heterotrophic culture. However, the results also show that activating PFP has little direct effect on heterotrophic carbohydrate metabolism beyond increasing the rate of cycling between hexose phosphates and triose phosphates.

Animals↗

Tobacco transformants with strongly decreased expression of pyrophosphate:fructose-6-phosphate expression in the base of their young growing leaves contain much higher levels of fructose-2,6-bisphosphate but no major changes in fluxes.

The role of pyrophosphate:fructose-6-phosphate 1-phosphotransferase (PFP) in developing leaves was studied using wild-type tobacco (Nicotiana tabacum L.) and transformants with decreased expression of PFP. (i) The leaf base, which is the youngest and most actively growing area of the leaf, had 2.5-fold higher PFP activity than the leaf tip. T3 transformants, with a 56-95% decrease in PFP activity in the leaf base and an 87-97% decrease in PFP activity in the leaf tip, were obtained by selfing and re-selfing individuals from two independent transformant lines. (ii) Other enzyme activities also showed a gradient from the leaf base to the leaf tip. There was a decrease in PFK and an increase in fructose-6-phosphate,2-kinase and plastidic fructose-1, 6-bisphosphatase, whereas cytosolic fructose-1,6-bisphosphatase activity was constant. None of these gradients was altered in the transformants. (iii) Fructose-2,6-bisphosphate (Fru2,6bisP) levels were similar at the base and tip of wild-type leaves in the dark. Illumination lead to a decrease in Fru2,6bisP at the leaf tip and an increase in Fru2,6bisP at the leaf base. Compared to wild-type plants, transformants with decreased expression of PFP had up to 2-fold higher Fru2,6bisP at the leaf tip in the dark, similar levels at the leaf tip in the light, 15-fold higher levels at the leaf base in the dark, and up to 4-fold higher levels at the leaf base in the light. (iv) To investigate metabolic fluxes, leaf discs were supplied with 14CO2 in the light or [14C]glucose in the light or the dark. Discs from the leaf tip had higher rates of photosynthesis than discs from the leaf base, whereas the rate of glucose uptake and metabolism was similar in both tissues. Significantly less label was incorporated into neutral sugars, and more into anionic compounds, cell wall and protein, and amino acids in discs from the leaf base. Metabolism of 14CO2 and [14C]glucose in transformants with low PFP was similar to that in wild-type plants, except that synthesis of neutral sugars from 14CO2 was slightly reduced in discs from the base of the leaf. (v) These results reveal that the role of PFP in the growing cells in the base of the leaf differs from that in mature leaf tissue. The increase in Fru2,6bisP in the light and the high activity of PFP relative to cytosolic fructose-1,6-bisphosphatase in the base of the leaf implicate PFP in the synthesis of sucrose in the light, as well as in glycolysis. The large increase in Fru2,6bisP at the base of the leaf of transformants implies that PFP plays a more important role in metabolism at the leaf base than in mature leaf tissue. Nevertheless, there were no major changes in carbon fluxes, or leaf or plant growth in transformants with below 10% of the wild-type PFP activity at the leaf base, implying that large changes in expression can be compensated by changes in Fru2,6-bisP, even in growing tissues.

Biological Transport↗

Calcium pyrophosphate dihydrate crystal deposition disease of the knee simulating spontaneous osteonecrosis.

A retrospective review of the frontal and lateral knee radiographs of 200 patients with calcium pyrophosphate dihydrate (CPPD) crystal deposition disease was performed. Of these 200 patients, nine patients (four male, five female, mean age 74 years, age range 63-87 years) had radiographic findings simulating osteonecrosis of the knee. One patient also had magnetic resonance imaging of the involved knee. A total of 10 knee radiographs in nine patients showed articular and periarticular calcification diagnostic of CPPD crystal deposition of the knee. In addition, all 10 radiographs showed flattening of one femoral condyle. Four of the 10 cases demonstrated an area of radiolucency in the subchondral bone surrounded by a halo of sclerosis. Eight of the 10 cases had narrowing of the involved joint compartment and osteophytosis. These findings mimic the radiographic signs of spontaneous osteonecrosis of the knee. In conclusion, flattening of the femoral condyles in CPPD crystal deposition disease simulates that of spontaneous osteonecrosis and probably relates to articular cartilage and meniscal damage that subsequently leads to stress fracture of subchondral bone with bone collapse.

Aged↗

Enzymatic systems of inorganic pyrophosphate bioenergetics in photosynthetic and heterotrophic protists: remnants or metabolic cornerstones?

An increasing body of biochemical and genetic evidence suggests that inorganic pyrophosphate (PPi) plays an important role in protist bioenergetics. In these organisms, two types of inorganic pyrophosphatases [EC 3.6.1.1, namely soluble PPases (sPPases) and proton-translocating PPases (H+-PPases)] that hydrolyse the PPi generated by cell anabolism, thereby replenishing the orthophosphate pool needed for phosphorylation reactions, are present in different cellular compartments. Photosynthetic and heterotrophic protists possess sPPases located in cellular organelles (plastids and mitochondria), where many anabolic and biosynthetic reactions take place, in addition to H+-PPases, which are integral membrane proteins of the vacuolysosomal membranes and use the chemical energy of PPi to generate an electrochemical proton gradient useful in cell bioenergetics. This last category of proton pumps was considered to be restricted to higher plants and some primitive photosynthetic bacteria, but it has been found recently in many protists (microalgae and protozoa) and bacteria, thus indicating that H+-PPases are much more widespread than previously thought. No cytosolic sPPase (in bacteria, fungi and animal cells) has been shown to occur in these lower eukaryotes. The widespread occurrence of these key enzymes of PPi metabolism among evolutionarily divergent protists strongly supports the ancestral character of the bioenergetics based on this simple energy-rich compound, which may play an important role in survival under different biotic and abiotic stress conditions.

Animals↗

Phosphate solubility and the cyanate-mediated synthesis of pyrophosphate.

The justification for a less alkaline primordial ocean (than present) is briefly reviewed, along with constraints on aqueous phosphate under such conditions. Based on the assumption that CaHPO(4) dihydrate determined the availability of phosphorus species, we have carried out laboratory simulations to determine equilibrium concentrations as a function of pH (in PIPES buffer) with added NaCl and CaCl(2). Consistent with expectations, solubility declines with higher pH and [CaCl(2)], but increases only slightly with [NaCl]. Significantly, PIPES shows no specific effect on the dissolution beyond its influence on pH and ionic strength. Data are also presented on the synthesis of pyrophosphate from the NaOCN/CaHPO(4).2H(2)O system, which could have provided a source of this phosphate anhydride on the early Earth.

Calcium Chloride↗

Pathogenesis of calcium pyrophosphate crystal deposition disease.

Calcium pyrophosphate dihydrate deposition (CPPDD) disease is an increasingly common form of arthritis affecting the elderly. It is characterized by the formation of CPPD crystals in articular cartilage and usually results in severe cartilage destruction with loss of joint function. This article discusses our understanding of how and why these crystals form, highlighting recent developments in the field.

Aged↗

Value and limitations of technetium-99m stannous pyrophosphate in the detection of acute myocardial infarction.

Technetium-99m stannous pyrophosphate (99mTc-PYP) myocardial imaging was performed in 436 consecutive patients for the evaluation of chest pain and suspected acute myocardial infarction (AMI). Scintigrams were assessed independently by three observers with a 90% interobserver agreement. In 134 patients with documented AMI (97 TRANSMURAL, 37 NONTRANSMURAL), THE SENSITIVITY OF 99MTc-PYP imaging was significantly lower in patients with nontransmural AMI (41%) than in patients with transmural AMI (78%), 99mTc-PYP imaging correctly localized the site of transmural infarction in 53 patients (70%). A diffuse 99mTc-PYP uptake was found in nine (10%) of 91 patients with positive scintigrams: six of these had a transmural AMI and three nontransmural AMI. In 226 patients without AMI, the specificity of infarct imaging was 95%. A false-positive scintigram was found in 0%, 8%, 9%, and 2% of patients with unstable angina, progressive angina, stable angina, and noncardiac chest pain, respectively. A diffuse uptake was found in six (54%) of 11 patients with false-positive scintigrams. No patient with the clinical diagnosis of noncardiac chest pain showed discrete uptake. In 76 patients with uncertain diagnosis for AMI, 99Tc-PYP imaging was considered of value in 11 patients with ventricular conduction defects (two patients with WPW syndrome, nine patients with LBBB). These data suggest that: 1. 99mTc-PYP imaging is moderately sensitive in detecting and localizing transmural AMI and is insensitive in detecting nontransmural AMI; 2. A discrete 99mTc-PYP uptake is highly specific for AMI; 3. a diffuse uptake is neither sensitive to, nor specific for AMI. Myocardial imaging with 99m-Tc-PYP is of clinical value when the standard electrocardiographic and enzymatic techniques are inadequate for an accurate diagnosis of AMI.

Acute Disease↗

Technetium-99m stannous pyrophosphate myocardial scintigrams in pericardial disease.

Technetium-99m stannous pyrophosphate (99mTc-PYP) myocardial scintigrams were obtained in 35 acute pericarditis and in three chronic constrictive pericarditis patients. Thirteen of 35 acute pericarditis patients (37%) and one of three chronic constrictive pericarditis patients (33%) had abnormal scintigrams (a diffuse pattern in eight patients and a regional pattern in six patients). Of the 17 acute pericarditis patients with classic ST-segment changes of acute pericarditis, 10 (56%) had abnormal scintigrams compared to three of 17 patients (18%) without these ECG changes (P less than 0.02). These data indicate that pericardial disease may cause an abnormal scintigram. Therefore, one must rule out pericardial disease before concluding that a positive scintigram is due to acute myocardial infarction.

Acute Disease↗

Improved detection of myocardial infarction with technetium-99m stannous pyrophosphate and serum MB creatine phosphokinase.

The relative sensitivity and combined value of myocardial technetium-99m stannous pyrophosphate imaging and determinations of serum MB creatine phosphokinase (the "myocardial" CPK isoenzyme) in detecting acute myocardial infarction were evaluated in 41 patients with suspected infarction and 23 patients recovering from cardiac surgery. In the patients with suspected infarction, myocardial infarction was confirmed in 25 and was consistently associated with increased serum MB CPK. Abnormal radionuclide images were obtained in 23 of 25 patients (92 percent) with definite myocardial infarction and in 2 of 16 patients without confirmed infarction. Although the localization of infarction by imaging correlated well with the localization by electrocardiogram, infarct size estimated by imaging did not correlate well with estimates based on peak total serum CPK activity or serial changes in CPK activity. Serum MB CPK activity increased after cardiac surgery in 6 patients undergoing valve replacement and in 17 patients undergoing coronary arterial bypass surgery. However, no patient with valve replacement and only 1 of the 17 with bypass surgery had an abnormal radionuclide image. These results suggest that (1) abnormal radionuclide images in patients without infarction can be distinguished from abnormal images indicative of ischemic necrosis by consideration of MB CPK activity and (2) interpretation of elevated MB CPK activity, particularly in particularly in patients undergoing cardiac surgery, is facilitated by evaluation with imaging.

Adult↗

Enzymatic method for continuous monitoring of inorganic pyrophosphate synthesis.

A sensitive method for the analysis of inorganic pyrophosphate (PPi) which utilizes the enzymes ATP sulfurylase and firefly luciferase is described. The assay is based on continuous monitoring of the ATP formed in the ATP sulfurylase reaction using purified firefly luciferase. The assay can be completed in less than 2 s and is not affected by inorganic phosphate. The method has been used for continuous monitoring of formation of PPi in Rhodospirillum rubrum chromatophores. The assay is extremely sensitive, the linear range of the assay being 1 X 10(-9) - 5 X 10(-7) M PPi. It is suitable for routine applications. It is also possible to use the method for determination of low amounts of adenosine 5'-phosphosulfate.

Bacterial Chromatophores↗

An assay for inorganic pyrophosphate in chondrocyte culture using anion-exchange high-performance liquid chromatography and radioactive orthophosphate labeling.

A method is described for determination of inorganic pyrophosphate (PPi) in cell culture medium and in rabbit articular chondrocytes grown in the presence of radioactive orthophosphate (32Pi). Intra- and extracellular 32PPi formed was measured using high-performance liquid chromatographic (HPLC) separation of the PPi from orthophosphate (Pi) and other phosphate-containing compounds. The chromatographic separation on a weak anion-exchange column is based on the extent to which various phosphate compounds form complexes with Mg2+ at low pH and the rate at which such formation occurs. These complexes are eluted more readily than the uncomplexed compounds. Best results were obtained using a simultaneous gradient of Mg2+ ions and ionic strength. In this case separation of small amounts of PPi from a large excess of Pi was possible without prior removal of Pi or extraction of the PPi fraction. The assay is also useful for measurement of inorganic pyrophosphatase activity. The sensitivity of the assay depends on the specific activity of the added 32Pi and on the culture conditions, but is comparable with the most sensitive of the enzymatic assays. Sample preparation, particularly deproteinization, proved to be of importance. The losses of PPi which occur during procedures of this sort due to hydrolysis and coprecipitation were quantitated.

Animals↗

Can biological calcification occur in the presence of pyrophosphate?

It was shown that it is apparently impossible for any calcification to occur in a system which contains a constant, physiological concentration of inorganic pyrophosphate. These results give further support to the earlier suggestion that inhibitors of calcium phosphate crystal growth must be removed from or denied access to the site of calcification to allow for the normal formation of the mineral phase. This study also suggests that the means of assessing the relative importance of a calcification inhibitor should be altered, since it is the equilibrium concentration of an inhibitor, and not its initial concentration in an assay system, which has physiological relevance.

Calcinosis↗

Site-specific rate constants for iron removal from diferric transferrin by nitrilotris(methylenephosphonic acid) and pyrophosphate.

The kinetics of iron removal from human serum diferric transferrin by nitrilotris(methylenephosphonic acid) (NTP) and pyrophosphate (PPi) have been studied in 0.1 M, pH 7.4, N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonate buffer at 25 degrees C using urea/polyacrylamide gel electrophoresis. The four microscopic rate constants required for a complete description of iron removal from the two transferrin metal-binding sites have been measured at 100 mM concentrations of NTP and PPi. There is very good agreement between the rate constants determined by electrophoresis in this study and the corresponding rate constants determined spectrophotometrically for monoferric transferrins that have been labeled at the empty binding site with substitutionally inert Co(III). The results validate the use of cobalt-labeled transferrins as models for kinetic studies on iron removal from diferric transferrin.

Cobalt↗

Redox active sulfhydryls are required for fructose 2,6-bisphosphate activation of plant pyrophosphate fructose-6-phosphate 1-phosphotransferase.

The classical, alpha/beta-subunit form (Q2) of green tomato pyrophosphate fructose-6-phosphate 1-phosphotransferase (PFP, EC 2.7.1.90), a cytosolic enzyme functional in carbohydrate metabolism, was rapidly inactivated on incubation with the oxidant 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB). Analysis of the DTNB-treated sample by a fluorescence procedure revealed that inactivation was accompanied by oxidation of sulfhydryl groups, primarily on the alpha-subunit. Phosphate metabolites--fructose 2,6-bisphosphate, fructose 1,6-bisphosphate, Pi, and PPi--protected against DTNB inactivation to varying degrees. The Km values for fructose 6-phosphate and PPi were not changed by DTNB treatment, but the capability for activation by fructose 2,6-bisphosphate was severely diminished. The oxidative inactivation of PFP was reversed by dithiothreitol, but not by monothiols (reduced glutathione or beta-mercaptoethanol). Reactivation was accompanied by restoration of the ability to undergo activation by fructose 2,6-bisphosphate. The findings suggest that sulfhydryl groups are essential for the activation of PFP by fructose 2,6-bisphosphate and raise the possibility that a reversible change in their redox status can take place under certain conditions. Evidence that this is the case was obtained with a preparation from wheat flour which, in the absence of an added oxidant, required reduction by a dithiol for activation by fructose 2,6-bisphosphate (dithiothreitol and reduced thioredoxin h).

Dithionitrobenzoic Acid↗

Effects of amino acids, adenine nucleotides and inorganic pyrophosphate on glutamine synthetase from Anabaena cylindrica.

Glutamine synthetase (L-glutamate:ammonia ligase (ADP-forming), EC 6.3.1.2) from Anabaena cylindrica was inhibited by alanine, glycine, serine and aspartate. The effects of alanine and serine were uncompetitive with respect to glutamate, while those of glycine and asparatate were uncompetitive with respect to glutamate, while those of glycine and aspartate were non-competitive and mixed type respectively. Different pairs of amino acids and their various combinations caused a cumulative inhibition of the enzyme activity. Glutamine synthetase was also inhibited by ADP and AMP and both nucleotides affected the enzyme competitively with respect to ATP and non-competitively for glutamate. Inorganic pyrophosphate, between 2 and 3 mM, produced a very pronounced inhibiton of enzyme activity. The inhibition by PPi was uncompetitive for ATP. Various combinations of the adenine nucleotides, PPi and Pi exerted a cumulative inhibitory effect on the enzyme activity, as did the amino acids, in different combinations with either adenine nucleotides, PPi or Pi. The effects of the adenine nucleotides and the amino acids were more pronounced at higher concentrations of ammonia. Except for serine similar responses of these effectors were obtained with increasing concentrations of Mg2+. It is proposed that changes in the free concentrations of Mg2+ are important in energy-dependent regulation of the enzyme activity in this alga.

Adenine Nucleotides↗

Pyrophosphate analogues as inhibitors of herpes simplex virus type 1 DNA polymerase.

Twenty nine pyrophosphate analogues have been tested for their ability to inhibit herpes simplex virus type 1 (HSV-1) DNA polymerase activity. The structural requirements for active inhibitors and their mechanism of action have been investigated. Active compounds had two negatively charged groups at close proximity. The most active compounds contained free phosphono and/or carboxyl groups. Apart from phosphonoformate and phosphonoacetate, which were strong inhibitors, some other analogues, 2-phosphonopropionate, 2-phenylphosphonoacetate, oxalate, carbonyldiphosphate, methanehydroxy-diphosphonate and hypophosphate also inhibited the HSV-1 DNA polymerase activity. With the exception of hypophosphate the tested compounds inhibited the activity of calf thymus DNA polymerase alpha to a lesser extent than the activity of the HSV-1 DNA polymerase. All inhibitors gave linear uncompetitive inhibition of HSV-1 DNA polymerase with activated DNA as variable substrate. With the four deoxynucleoside triphosphates as variable substrates all inhibitors except hypophosphate gave linear non-competitive inhibition patterns. Hypophosphate caused a more competitive type of inhibition. The inhibition constants for the active compounds have been determined. Phosphonoformate, phosphonoacetate, methanehydroxydiphosphonate and hypophosphate also inhibited HSV-1 plaque formation in cell culture.

Animals↗