Exopolyphosphatase Activity Research Articles

Purification, crystallization and X-ray crystallographic analysis of a putative exopolyphosphatase from Zymomonas mobilis.

Exopolyphosphatase (PPX) enzymes degrade inorganic polyphosphate (poly-P), which is essential for the survival of microbial cells in response to external stresses. In this study, a putative exopolyphosphatase from Zymomonas mobilis (ZmPPX) was crystallized. Crystals of the wild-type enzyme diffracted to 3.3 Å resolution and could not be optimized further. The truncation of 29 amino acids from the N-terminus resulted in crystals that diffracted to 1.8 Å resolution. The crystals belonged to space group C2, with unit-cell parameters a = 122.0, b = 47.1, c = 89.5 Å, α = γ = 90, β = 124.5°. An active-site mutant that crystallized in the same space group and with similar unit-cell parameters diffracted to 1.56 Å resolution. One molecule was identified per asymmetric unit. Analytical ultracentrifugation confirmed that ZmPPX forms a dimer in solution. It was confirmed that ZmPPX possesses exopolyphosphatase activity against a synthetic poly-P substrate.

Polyphosphatase PPN1 of <i>Saccharomyces cerevisiae</i> Is a Deoxyadenosine Triphosphate Phosphohydrolase

The Saccharomyces cerevisiae polyphosphatase PPN1 (uniprot/Q04119) degrades inorganic polyphosphates both by cleaving Pi from the chain end and by fragmenting long-chain polymers into shorter ones. In this study, we have found a new activity of this protein: it releases phosphate from dATP. The dATP phosphohydrolase activity of pure PPN1 was ~7-fold lower compared to the exopolyphosphatase activity. This activity was strongly stimulated by Co2+ ions, as well as by ammonium ions, and inhibited by heparin and pyrophosphate similar to the exopolyphosphatase activity of PPN1. The Km value for dATP was 0.88 ± 0.14 mM. The dATP phosphohydrolase activity in the cells of PPN1-overexpressing yeast strain was several-fold higher than that in the parent strain. The other exopolyphosphatase of S. cerevisiae, PPX1, did not split Pi from dATP.

A soluble pyrophosphatase is essential to oogenesis and is required for polyphosphate metabolism in the red flour beetle (Tribolium castaneum).

Polyphosphates have been found in all cell types examined to date and play diverse roles depending on the cell type. In eukaryotic organisms, polyphosphates have been mainly investigated in mammalian cells with few studies on insects. Some studies have demonstrated that a pyrophosphatase regulates polyphosphate metabolism, and most of them were performed on trypanosomatids. Here, we investigated the effects of sPPase gene knocked down in oogenesis and polyphosphate metabolism in the red flour beetle (Tribolium castaneum) A single sPPase gene was identified in insect genome and is maternally provided at the mRNA level and not restricted to any embryonic or extraembryonic region during embryogenesis. After injection of Tc-sPPase dsRNA, female survival was reduced to 15% of the control (dsNeo RNA), and egg laying was completely impaired. The morphological analysis by nuclear DAPI staining of the ovarioles in Tc-sPPase dsRNA-injected females showed that the ovariole number is diminished, degenerated oocytes can be observed, and germarium is reduced. The polyphosphate level was increased in cytoplasmic and nuclear fractions in Tc-sPPase RNAi; Concomitantly, the exopolyphosphatase activity decreased in both fractions. Altogether, these data suggest a role for sPPase in the regulation on polyphosphate metabolism in insects and provide evidence that Tc-sPPase is essential to oogenesis.

Polyphosphatase PPN1 of Saccharomyces cerevisiae: switching of exopolyphosphatase and endopolyphosphatase activities.

The polyphosphatase PPN1 of Saccharomyces cerevisiae shows an exopolyphosphatase activity splitting phosphate from chain end and an endopolyphosphatase activity fragmenting high molecular inorganic polyphosphates into shorter polymers. We revealed the compounds switching these activities of PPN1. Phosphate release and fragmentation of high molecular polyphosphate prevailed in the presence of Co2+ and Mg2+, respectively. Phosphate release and polyphosphate chain shortening in the presence of Co2+ were inhibited by ADP but not affected by ATP and argininе. The polyphosphate chain shortening in the presence of Mg2+ was activated by ADP and arginine but inhibited by ATP.

PPX1 gene overexpression has no influence on polyphosphates in Saccharomyces cerevisiae.

The role of exopolyphosphatase PPX1 in polyphosphate metabolism in yeasts has been studied in strains of Saccharomyces cerevisiae with inactivated PPX1 and PPN1 genes transformed by the expression vector carrying the yeast PPX1 gene. Exopolyphosphatase activity in transformant strains increased 90- and 40-fold compared to the ΔPPX1 and ΔPPN1 strains, respectively. The purified recombinant exopolyphosphatase PPX1 was similar to the PPX1 of wild strains in its substrate specificity and requirement for divalent metal cations. It was more active with tripolyphosphate and low molecular mass polyphosphates than with high molecular mass polyphosphates and required Mg2+ for its activity. The high level of recombinant PPX1 expression caused no decrease in polyphosphate content in the cells of the transformant. This fact suggests the restricted role of PPX1 in polyphosphate metabolism in yeasts.

Purification and properties of recombinant exopolyphosphatase PPN1 and effects of its overexpression on polyphosphate in Saccharomyces cerevisiae

Inorganic polyphosphate performs many regulatory functions in living cells. The yeast exopolyphosphatase PPN1 is an enzyme with multiple cellular localization and probably variable functions. The Saccharomyces cerevisiae strain with overexpressed PPN1 was constructed for large-scale production of the enzyme and for studying the effect of overproduction on polyphosphate metabolism. The ΔPPN1 strain was transformed by the vector containing this gene under a strong constitutive promoter of glycerol aldehyde-triphosphate dehydrogenase of S.cerevisiae. Exopolyphosphatase activity in the transformant increased 28- and 11-fold compared to the ΔPPN1 and parent strains, respectively. The content of acid-soluble polyphosphate decreased ∼6-fold and the content of acid-insoluble polyphosphate decreased ∼2.5-fold in the cells of the transformant compared to the ΔPPN1 strain. The recombinant enzyme was purified. The substrate specificity, cation requirement, and inhibition by heparin were found to be similar to native PPN1. The molecular mass of a subunit (∼33 kD) and the amino acid sequence of the recombinant enzyme were the same as in mature PPN1. The recombinant enzyme was localized mainly in the cytoplasm (40%) and vacuoles (20%). The overproducer strain had no growths defects under phosphate deficiency or phosphate excess. In contrast to the parent strains accumulating polyphosphate, the transformant accumulated orthophosphate under phosphate surplus.

Synthesis and evaluation of chromogenic and fluorogenic substrates for high-throughput detection of enzymes that hydrolyze inorganic polyphosphate.

Inorganic polyphosphates, linear polymers of orthophosphate, occur naturally throughout biology and have many industrial applications. Their biodegradable nature makes them attractive for a multitude of uses, and it would be important to understand how polyphosphates are turned over enzymatically. Studies of inorganic polyphosphatases are, however, hampered by the lack of high-throughput methods for detecting and quantifying rates of polyphosphate degradation. We now report chromogenic and fluorogenic polyphosphate substrates that permit spectrophotometric monitoring of polyphosphate hydrolysis and allow for high-throughput analyses of both endopolyphosphatase and exopolyphosphatase activities, depending on assay configuration. These substrates contain 4-nitrophenol or 4-methylumbelliferone moieties that are covalently attached to the terminal phosphates of polyphosphate via phosphoester linkages formed during reactions mediated by EDAC (1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide). This report identifies Nudt2 as an inorganic polyphosphatase and also adds to the known coupling chemistry for polyphosphates, permitting facile covalent linkage of alcohols with the terminal phosphates of inorganic polyphosphate.

Temperature influence on biological phosphorus removal induced by aerobic/extended-idle regime

Previous researches have demonstrated that biological phosphorus removal (BPR) from wastewater could be driven by the aerobic/extended-idle (A/EI) regime. This study further investigated temperature effects on phosphorus removal performance in six A/EI sequencing batch reactors (SBRs) operated at temperatures ranging from 5 to 30°C. The results showed that phosphorus removal efficiency increased with temperature increasing from 5 to 20°C but slightly decreased when temperature continually increased to 30°C. The highest phosphorus removal rate of 97.1% was obtained at 20°C. The biomass cultured at 20°C contained more polyphosphate accumulating organisms (PAO) and less glycogen accumulating organisms (GAO) than that cultured at any other temperatures investigated. The mechanism studies revealed that temperature affected the transformations of glycogen and polyhydroxyalkanoates, and the activities of exopolyphosphatase and polyphosphate kinase activities. In addition, phosphorus removal performances of the A/EI and traditional anaerobic/oxic (A/O) SBRs were compared at 5 and 20°C, respectively. The results showed the A/EI regime drove better phosphorus removal than the A/O regime at both 5 and 20°C, and more PAO and less GAO abundances in the biomass might be the principal reason for the higher BPR in the A/EI SBRs as compared with the A/O SBRs.

Polyphosphates and exopolyphosphatase activities in the yeast Saccharomyces cerevisiae under overexpression of homologous and heterologous PPN1 genes

The role of exopolyphosphatase PPN1 in polyphosphate metabolism in fungi has been studied in strains of Saccharomyces cerevisiae transformed by the yeast PPN1 gene and its ortholog of the fungus Acremonium chrysogenum producing cephalosporin C. The PPN1 genes were expressed under a strong constitutive promoter of the gene of glycerol aldehyde-triphosphate dehydrogenase of S. cerevisiae in the vector pMB1. The yeast strain with inactivated PPN1 gene was transformed by the above vectors containing the PPN1 genes of S. cerevisiae and A. chrysogenum. Exopolyphosphatase activity in the transformant with the yeast PPN1 increased 28- and 11-fold compared to the mutant and parent PPN1 strains. The amount of polyphosphate in this transformant decreased threefold. Neither the increase in exopolyphosphatase activity nor the decrease in polyphosphate content was observed in the transformant with the orthologous PPN1 gene of A. chrysogenum, suggesting the absence of the active form of PPN1 in this transformant.

Long-term performance of enhanced biological phosphorus removal with increasing concentrations of silver nanoparticles and ions

The wide use of silver nanoparticles (AgNPs) and silver ions (Ag+) as antimicrobial agents have caused concerns about their potential effects on the environment, such as wastewater treatment plants. This paper reports the effects of increasing the influent AgNPs and Ag+ from 1 to 5 mg L−1 on the performance of enhanced biological phosphorus removal (EBPR). The increase of AgNPs showed no significant influence on EBPR in both short-term and long-term experiments. Phosphorus removal, however, was decreased by a sudden increase in Ag+ concentration and it was gradually recovered after long-term culture. The mechanism studies showed that the transformation of polyhydroxyalkanoates and glycogen and the activity of exopolyphosphatase declined when Ag+ was increased suddenly, but they were recovered after long-term culture. The denatured gradient gel electrophoresis and fluorescence in situ hybridization analyses indicated that the bacterial community structure and the abundance of polyphosphate accumulation organisms were not changed by AgNPs or Ag+. Further investigations revealed that the long-term exposure of Ag+ increased the amount of sludge extracellular polymeric substances, which accounted for the mitigation of Ag+ toxicity to the EBPR key enzyme and microbes.

Inorganic Polyphosphates Regulate Hexokinase Activity and Reactive Oxygen Species Generation in Mitochondria of Rhipicephalus (Boophilus) microplus Embryo

The physiological roles of polyphosphates (poly P) recently found in arthropod mitochondria remain obscure. Here, the possible involvement of poly P with reactive oxygen species generation in mitochondria of Rhipicephalus microplus embryos was investigated. Mitochondrial hexokinase and scavenger antioxidant enzymes, such as superoxide dismutase, catalase, and glutathione reductase were assayed during embryogenesis of R. microplus. The influence of poly P3 and poly P15 were analyzed during the period of higher enzymatic activity during embryogenesis. Both poly Ps inhibited hexokinase activity by up to 90% and, interestingly, the mitochondrial membrane exopolyphosphatase activity was stimulated by the hexokinase reaction product, glucose-6-phosphate. Poly P increased hydrogen peroxide generation in mitochondria in a situation where mitochondrial hexokinase is also active. The superoxide dismutase, catalase and glutathione reductase activities were higher during embryo cellularization, at the end of embryogenesis and during embryo segmentation, respectively. All of the enzymes were stimulated by poly P3. However, superoxide dismutase was not affected by poly P15, catalase activity was stimulated only at high concentrations and glutathione reductase was the only enzyme that was stimulated in the same way by both poly Ps. Altogether, our results indicate that inorganic polyphosphate and mitochondrial membrane exopolyphosphatase regulation can be correlated with the generation of reactive oxygen species in the mitochondria of R. microplus embryos.

The Two PPX-GppA Homologues from Mycobacterium tuberculosis Have Distinct Biochemical Activities

Inorganic polyphosphate (poly-P), guanosine pentaphosphate (pppGpp) and guanosine tetraphosphate (ppGpp) are ubiquitous in bacteria. These molecules play a variety of important physiological roles associated with stress resistance, persistence, and virulence. In the bacterial pathogen Mycobacterium tuberculosis, the identities of the proteins responsible for the metabolism of polyphosphate and (p)ppGpp remain to be fully established. M. tuberculosis encodes two PPX-GppA homologues, Rv0496 (MTB-PPX1) and Rv1026, which share significant sequence similarity with bacterial exopolyphosphatase (PPX) and guanosine pentaphosphate 5′-phosphohydrolase (GPP) proteins. Here we delineate the respective biochemical activities of the Rv0496 and Rv1026 proteins and benchmark these against the activities of the PPX and GPP proteins from Escherichia coli. We demonstrate that Rv0496 functions as an exopolyphosphatase, showing a distinct preference for relatively short-chain poly-P substrates. In contrast, Rv1026 has no detectable exopolyphosphatase activities. Analogous to the E. coli PPX and GPP enzymes, the exopolyphosphatase activities of Rv0496 are inhibited by pppGpp and, to a lesser extent, by ppGpp alarmones, which are produced during the bacterial stringent response. However, neither Rv0496 nor Rv1026 have the ability to hydrolyze pppGpp to ppGpp; a reaction catalyzed by E. coli PPX and GPP. Both the Rv0496 and Rv1026 proteins have modest ATPase and to a lesser extent ADPase activities. pppGpp alarmones inhibit the ATPase activities of Rv1026 and, to a lesser extent, the ATPase activities of Rv0496. We conclude that PPX-GppA family proteins may not possess all the catalytic activities implied by their name and may play distinct biochemical roles involved in polyphosphate and (p)ppGpp metabolic pathways.

Calcium- and polyphosphate-containing acidic granules of sea urchin eggs are similar to acidocalcisomes, but are not the targets for NAADP

Acidocalcisomes are acidic calcium-storage compartments described from bacteria to humans and characterized by their high content in poly P (polyphosphate), a linear polymer of many tens to hundreds of Pi residues linked by high-energy phosphoanhydride bonds. In the present paper we report that millimolar levels of short-chain poly P (in terms of Pi residues) and inorganic PPi are present in sea urchin extracts as detected using 31P-NMR, enzymatic determinations and agarose gel electrophoresis. Poly P was localized to granules randomly distributed in the sea urchin eggs, as shown by labelling with the poly-P-binding domain of Escherichia coli exopolyphosphatase. These granules were enriched using iodixanol centrifugation and shown to be acidic and to contain poly P, as determined by Acridine Orange and DAPI (4′,6′-diamidino-2-phenylindole) staining respectively. These granules also contained large amounts of calcium, sodium, magnesium, potassium and zinc, as detected by X-ray microanalysis, and bafilomycin A1-sensitive ATPase, pyrophosphatase and exopolyphosphatase activities, as well as Ca2+/H+ and Na+/H+ exchange activities, being therefore similar to acidocalcisomes described in other organisms. Calcium release from these granules induced by nigericin was associated with poly P hydrolysis. Although NAADP (nicotinic acid–adenine dinucleotide phosphate) released calcium from the granule fraction, this activity was not significantly enriched as compared with the NAADP-stimulated calcium release from homogenates and was not accompanied by poly P hydrolysis. GPN (glycyl-L-phenylalanine-naphthylamide) released calcium when added to sea urchin homogenates, but was unable to release calcium from acidocalcisome-enriched fractions, suggesting that these acidic stores are not the targets for NAADP.

The patterns of utilization and accumulation of polyphosphates in the cytosol of the yeast Saccharomyces cerevisiae under inactivation of exopolyphosphatase genes PPX1 and PPN1

The effect of inactivation of the PPX1 and PPN1 genes encoding the yeast exopolyphosphatases on the activities of these enzymes and polyphosphate content in the cytosol of Saccharomyces cerevisiae was studied under Pi deficit and Pi excess in the cultivation medium. Under Pi deficit, exopolyphosphatase activity in strain CRN (with inactivated PPN1 gene) and in the parent strain CRY increased 3- and 1.5-fold, respectively. In the strain CRX (with inactivated PPX1 gene), exopolyphosphatase activity did not change under Pi deficit. Transfer from Pi-deficient to Pi-rich medium was accompanied by an ∼1.7-fold increase of exopolyphosphatase activities in the cytosol preparations of strains CRY, CRX, and CRN. In the cytosol of the double mutant, exopolyphosphatase activity was practically absent under all of the above cultivation conditions. The content of polyphosphates in the cytosol preparations of all strains under study substantially decreased under Pi deficit. Transfer from Pi-deficient to Pi-rich medium was accompanied by polyphosphate over-accumulation only in the cytosol preparations of stains CRX and CNX, where their levels increased ∼1.3 and 3.5-fold, respectively. No over-accumulation was observed in the parent strain CRY and in the PPN1-deficient strain CRN. These data suggest that the exopolyphosphatases encoded by the PPX1 and PPN1 genes are not involved in polyphosphate synthesis.

Exopolyphosphatases PPX1 and PPX2 from Corynebacterium glutamicum

Corynebacterium glutamicum accumulates up to 300 mM of inorganic polyphosphate (PolyP) in the cytosol or in granules. The gene products of cg0488 (ppx1) and cg1115 (ppx2) were shown to be active as exopolyphosphatases (PPX), as overexpression of either gene resulted in higher exopolyphosphatase activities in crude extracts and deletion of either gene with lower activities than those of the wild-type strain. PPX1 and PPX2 from C. glutamicum share only 25% identical amino acids and belong to different protein groups, which are distinct from enterobacterial, archaeal, and yeast exopolyphosphatases. In comparison to that in the wild type, more intracellular PolyP accumulated in the Deltappx1 and Deltappx2 deletion mutations but less when either ppx1 or ppx2 was overexpressed. When C. glutamicum was shifted from phosphate-rich to phosphate-limiting conditions, a growth advantage of the deletion mutants and a growth disadvantage of the overexpression strains compared to the wild type were observed. Growth experiments, exopolyphosphatase activities, and intracellular PolyP concentrations revealed PPX2 as being a major exopolyphosphatase from C. glutamicum. PPX2(His) was purified to homogeneity and shown to be active as a monomer. The enzyme required Mg2+ or Mn2+ cations but was inhibited by millimolar concentrations of Mg2+, Mn2+, and Ca2+. PPX2 from C. glutamicum was active with short-chain polyphosphates, even accepting pyrophosphate, and was inhibited by nucleoside triphosphates.

Inactivation of PPX1 and PPN1 genes encoding exopolyphosphatases of Saccharomyces cerevisiae does not prevent utilization of polyphosphates as phosphate reserve

Cytosol polyphosphates (polyPs) are the main phosphate (P(i)) reserve in the yeast Saccharomyces cerevisiae. In this work, the participation of cytosol polyPs and exopolyphosphatases in maintenance of P(i) homeostasis under P(i) deficit in the cultivation medium has been studied in different strains of S. cerevisiae. The growth of yeast strains with inactivated genes PPX1 and PPN1 encoding the yeast exopolyphosphatases and a strain with double mutations in these genes in a P(i)-deficient medium is not disturbed. All the studied strains are able to maintain relatively constant P(i) levels in the cytosol. In P(i)-deficient medium, polyP hydrolysis in the cytosol of the parent and PPN1-deficient strains seems to be performed by exopolyphosphatase Ppx1 and proceeds without any change of the spectrum of polyP chain lengths. In the PPX1-deficient strain, long-chain polyPs are depleted first, and only then short-chain polyPs are hydrolyzed. In the double PPX1 and PPN1 mutant having low exopolyphosphatase activity, polyP hydrolysis in the cytosol starts with a notable delay, and about 20% of short-chain polyPs still remain after the polyP hydrolysis in other strains has almost been completed. This fact suggests that S. cerevisiae possesses a system, which makes it possible to compensate for inactivation of the PPX1 and PPN1 genes encoding exopolyphosphatases of the yeast cells.

Human Metastasis Regulator Protein H-Prune is a Short-Chain Exopolyphosphatase

The DHH superfamily human protein h-prune, a binding partner of the metastasis suppressor nm23-H1, is frequently overexpressed in metastatic cancers. From an evolutionary perspective, h-prune is very close to eukaryotic exopolyphosphatases. Here, we show for the first time that h-prune efficiently hydrolyzes short-chain polyphosphates (k cat of 3-40 s (-1)), including inorganic tripoly- and tetrapolyphosphates and nucleoside 5'-tetraphosphates. Long-chain inorganic polyphosphates (>or=25 phosphate residues) are converted more slowly, whereas pyrophosphate and nucleoside triphosphates are not hydrolyzed. The reaction requires a divalent metal cofactor, such as Mg (2+), Co (2+), or Mn (2+), which activates both the enzyme and substrate. Notably, the exopolyphosphatase activity of h-prune is suppressed by nm23-H1, long-chain polyphosphates and pyrophosphate, which may be potential physiological regulators. Nucleoside triphosphates, diadenosine hexaphosphate, cAMP, and dipyridamole (inhibitor of phosphodiesterase) do not affect this activity. Mutation of seven single residues corresponding to those found in the active site of yeast exopolyphosphatase led to a severe decrease in h-prune activity, whereas one variant enzyme exhibited enhanced activity. Our results collectively suggest that prune is the missing exopolyphosphatase in animals and support the hypothesis that the metastatic effects of h-prune are modulated by inorganic polyphosphates, which are increasingly recognized as critical regulators in cells.

Exopolyphosphatases in nuclear and mitochondrial fractions during embryogenesis of the hard tick Rhipicephalus ( Boophilus) microplus

The present work evaluated polyphosphate (poly P) metabolism in nuclear and mitochondrial fractions during Rhipicephalus microplus embryogenesis. Nuclear poly P decreased and activity of exopolyphosphatase (PPX — polyphosphate–phosphohydrolases; EC 3.6.1.11) increased after embryo cellularization until the end of embryogenesis. The utilization of mitochondrial poly P content occurred between embryo cellularization and segmentation stages. Increasing amounts of total RNA extracted from eggs progressively enhanced nuclear PPX activity, whereas it exerted no effect on mitochondrial PPX activity. The decline in total poly P content after the 7th day of embryogenesis does not reflect the free P i increase and the total poly P chain length decrease after embryo cellularization. The Km app utilizing poly P 3, poly P 15 and poly P 65 as substrate was almost the same for the nuclear fraction (around 1μM), while the affinity for substrate in mitochondrial fraction was around 10 times higher for poly P 3 (Km app = 0.2μM) than for poly P 15 (Km app = 2.8μM) and poly P 65 (Km app = 3.6μM). PPX activity was stimulated by a factor of two by Mg 2+ and Co 2+ in the nuclear fraction and only by Mg 2+ in the mitochondrial fraction. Heparin (20µg/mL) inhibited nuclear and mitochondrial PPX activity in about 90 and 95% respectively. Together, these data are consistent with the existence of two different PPX isoforms operating in the nuclei and mitochondria of the hard tick R. microplus with distinct metal dependence, inhibitor and activator sensitivities. The data also shed new light on poly P biochemistry during arthropod embryogenesis, opening new routes for future comparative studies on the physiological roles of different poly P pools distributed over cell compartments.

Polyphosphates and exopolyphosphatases in cytosol and mitochondria of Saccharomyces cerevisiae during growth on glucose or ethanol under phosphate surplus

Content and chain lengths of inorganic polyphosphates (polyP) as well as exopolyphosphatase activities were compared in cytosol and mitochondria of the yeast Saccharomyces cerevisiae during growth on glucose or ethanol under phosphate surplus. PolyP metabolism in cytosol and mitochondria was substantially dependent upon the carbon source. Acid-soluble polyP accumulated mainly in cytosol using either glucose or ethanol. The level of the accumulation was lower during growth on ethanol compared to that on glucose. Increase in polyP content in mitochondria was observed during growth on glucose, but not on ethanol. In cytosol the activity of exopolyphosphatase PPN1 was increased and the activity of exopolyphosphatase PPX1 was decreased independently of the carbon source under phosphate surplus conditions. Growth on ethanol caused exopolyphosphatase PPN1 to appear in the soluble mitochondrial fraction, while during growth on glucose only exopolyphosphatase PPX1 was present in this fraction.

A mitochondrial exopolyphosphatase activity modulated by phosphate demand in Rhipicephalus ( Boophilus) microplus embryo

This study describes Exopolyphosphatases (PPX) activity in mitochondria of Rhipicephalus microplus embryos. Mitochondria were isolated by differential centrifugation and PPX activity was analyzed through the hydrolysis of the substrate Polyphosphate (Poly P 15). We investigated the influence of NADH, NAD +, P i and ADP in a concentration range of 0.1–2.0 mM. Poly P hydrolysis was stimulated about two-fold by NADH and strongly inhibited by P i. The PPX activity also increased in the presence of the respiratory substrates pyruvic and succinic acids, and this stimulatory effect disappeared upon addition of KCN. Mitochondrial respiration was activated by ADP using poly P as the only source of P i. Endogenous poly P content changed following PPX activity during embryogenesis from the first up to 18th day of development. The data describe exopoly P as being modulated by P i demand and related to energy supply during embryogenesis of hard ticks.