Loss of renal phosphate wasting in a child with autosomal dominant hypophosphatemic rickets caused by a FGF23 mutation.

A girl with autosomal dominant hypophosphatemic rickets, presented with clinical, radiological and laboratory signs of rickets at the age of 11 months. She showed a good response to the treatment with low doses of oral phosphate and calcitriol. Surprisingly, she lost her renal phosphate wasting at the age of 8 years, indicating that the disturbed phosphate metabolism can be compensated by hormonal or other factors.     

Impact of MtrA on phosphate metabolism genes and the response to altered phosphate conditions in Streptomyces

Phosphate metabolism is known to be regulated by the PhoPR regulatory system in Streptomyces and some other bacteria. In this study, we report that MtrA also regulates phosphate metabolism in Streptomyces. Our data showed that, in Streptomyces coelicolor, MtrA regulates not only phosphate metabolism genes such as phoA but also phoP under different phosphate conditions, including growth on rich complex media without added inorganic phosphate and on defined media with low or high concentrations of inorganic phosphate. Cross-regulation was also observed among mtrA, phoP and glnR under these conditions. We demonstrated both in vitro and in vivo binding of MtrA to the promoter regions of genes associated with phosphate metabolism and to the intergenic region between phoR and phoU, indicating that these phosphate metabolism genes are targets of MtrA. We further showed that MtrA in S. lividans and S. venezuelae has detectable regulatory effects on expression of phosphate metabolism genes. Additionally, the MtrA homologue from Corynebacterium glutamicum bound predicted MtrA sites of multiple phosphate metabolism genes, implying its potential for regulating phosphate metabolism in this species. Overall, our findings support MtrA as a major regulator for phosphate metabolism in Streptomyces and also potentially in other actinobacteria.     

The control of plant glutamate dehydrogenase by pyridoxal-5′-phosphate

The proposition that the nitrogen status of a plant is reflected by the ratio pyridoxal phosphate to pyridoxamine phosphate and that this ratio exerts a controlling influence on plant metabolism has been examined. The ratio pyridoxal phosphate to pyridoxamine phosphate has been shown to increase during nitrogen starvation. The inhibition of glutamate dehydrogenase by pyridoxal phosphate has been examined and the kinetics of inhibition are discussed in relation to the proposed control of metabolism.     

Changes in high-energy phosphate metabolites in loaches (cobitis biwae) during 2-phenoxyethanol anesthesia

1. We evaluated changes in high-energy phosphate metabolism in the muscle of loaches during 2-phenoxyethanol (2-PE) anesthesia by ³¹P-NMR.2. The creatine phosphate (PCr) concentration increased while the inorganic phosphate (Pi) concentration decreased in the muscle as 2-PE anesthesia was continued, but both returned to the preanesthetic values with recovery from the anesthesia.3. The sugar phosphate (SP) concentration also increased during anesthesia, but SP did not disappear after recovery.4. In the muscle of loaches anesthetized with 2-PE, the phosphate metabolism was aerobic, but carbohydrate metabolism was suppressed.     

Hypoglycosylation due to dolichol metabolism defects

Dolichol phosphate is a lipid carrier embedded in the endoplasmic reticulum (ER) membrane essential for the synthesis of N-glycans, GPI-anchors and protein C- and O-mannosylation. The availability of dolichol phosphate on the cytosolic site of the ER is rate-limiting for N-glycosylation. The abundance of dolichol phosphate is influenced by its de novo synthesis and the recycling of dolichol phosphate from the luminal leaflet to the cytosolic leaflet of the ER. Enzymatic defects affecting the de novo synthesis and the recycling of dolichol phosphate result in glycosylation defects in yeast or cell culture models, and are expected to cause glycosylation disorders in humans termed congenital disorders of glycosylation (CDG). Currently only one disorder affecting the dolichol phosphate metabolism has been described. In CDG-Im, the final step of the de novo synthesis of dolichol phosphate catalyzed by the enzyme dolichol kinase is affected. The defect causes a severe phenotype with death in early infancy. The present review summarizes the biosynthesis of dolichol-phosphate and the recycling pathway with respect to possible defects of the dolichol phosphate metabolism causing glycosylation defects in humans.     

A second target of the antimalarial and antibacterial agent fosmidomycin revealed by cellular metabolic profiling

Antimicrobial drug resistance is an urgent problem in the control and treatment of many of the world's most serious infections, including Plasmodium falciparum malaria, tuberculosis, and healthcare-associated infections with Gram-negative bacteria. Because the non-mevalonate pathway of isoprenoid biosynthesis is essential in eubacteria and P. falciparum and this pathway is not present in humans, there is great interest in targeting the enzymes of non-mevalonate metabolism for antibacterial and antiparasitic drug development. Fosmidomycin is a broad-spectrum antimicrobial agent currently in clinical trials of combination therapies for the treatment of malaria. In vitro, fosmidomycin is known to inhibit the deoxyxylulose phosphate reductoisomerase (DXR) enzyme of isoprenoid biosynthesis from multiple pathogenic organisms. To define the in vivo metabolic response to fosmidomycin, we developed a novel mass spectrometry method to quantitate six metabolites of non-mevalonate isoprenoid metabolism from complex biological samples. Using this technique, we validate that the biological effects of fosmidomycin are mediated through blockade of de novo isoprenoid biosynthesis in both P. falciparum malaria parasites and Escherichia coli bacteria: in both organisms, metabolic profiling demonstrated a block of isoprenoid metabolism following fosmidomycin treatment, and growth inhibition due to fosmidomycin was rescued by media supplemented with isoprenoid metabolites. Isoprenoid metabolism proceeded through DXR even in the presence of fosmidomycin but was inhibited at the level of the downstream enzyme, methylerythritol phosphate cytidyltransferase (IspD). Overexpression of IspD in E. coli conferred fosmidomycin resistance, and fosmidomycin was found to inhibit IspD in vitro. This work has validated fosmidomycin as a biological reagent for blocking non-mevalonate isoprenoid metabolism and suggests a second in vivo target for fosmidomycin within isoprenoid biosynthesis, in two evolutionarily diverse pathogens.     

Loss of PiT-2 results in abnormal bone development and decreased bone mineral density and length in mice

Normal bone mineralization requires phosphate oversaturation in bone matrix vesicles, as well as normal regulation of phosphate metabolism via the interplay among bone, intestine, and kidney. In turn, derangement of phosphate metabolism greatly affects bone function and structure. The type III sodium-dependent phosphate transporters, PiT-1 and PiT-2, are believed to be important in tissue phosphate metabolism and physiological bone formation, but their requirement and molecular roles in bone remain poorly investigated. In order to decipher the role of PiT-2 in bone, we examined normal bone development, growth, and mineralization in global PiT-2 homozygous knockout mice. PiT-2 deficiency resulted in reduced vertebral column, femur, and tibia length as well as mandibular dimensions. Micro-computed tomography analysis revealed that bone mineral density in the mandible, femur, and tibia were decreased, indicating that maintenance of bone function and structure is impaired in both craniofacial and long bones of PiT-2 deficient mice. Both cortical and trabecular thickness and mineral density were reduced in PiT-2 homozygous knockout mice compared with wild-type mice. These results suggest that PiT-2 is involved in normal bone development and growth and plays roles in cortical and trabecular bone metabolism feasibly by regulating local phosphate transport and mineralization processes in the bone. Further studies that evaluate bone cell-specific loss of PiT-2 are now warranted and may yield insight into complex mechanisms of bone development and growth, leading to identification of new therapeutic options for patients with bone diseases.     

The effects of acute phosphate depletion on isolated chick kidney tubule cells

Isolated tubule cells from chick kidney respond to a short period of phosphate deprivation with increased phosphate uptake and a resistance to parathyroid hormone. During phosphate depletion a considerable amount of phosphate may be released from the cells, but intracellular inorganic phosphate levels are maintained by the hydrolysis of organic phosphate esters. It is suggested that the concomitant changes in metabolism might act as the signal causing the onset of the changes in phosphate handling associated with phosphate deprivation.     

The conversion of pyridoxine phosphate into pyridoxal phosphate in Escherichia coli

1. Evidence is presented for the presence of pyridoxine phosphate oxidase in aqueous extracts of Escherichia coli. Some comparison is made with pyridoxamine phosphate oxidase. 2. Isoniazid and iproniazid were found to combine with pyridoxal phosphate, but isoniazid did not combine with either pyridoxamine phosphate or pyridoxine phosphate. Both oxidase activities were somewhat inhibited by benzylamine and putrescine, but not by phenethylamine or cadaverine. 3. The significance of pyridoxine phosphate oxidase in cell metabolism is discussed.     

Application of polyphosphate metabolism to environmental and biotechnological problems

The synthesis and degradation of polyphosphate (polyP) are influenced by the energy state of the cell and extracellular phosphate levels. The import of excess phosphate and its incorporation into polyP under phosphate- and energy-rich growth conditions allows organisms to survive when phosphate or energy are depleted. Under phosphate-starvation conditions, phosphate can be recovered from polyP by hydrolysis. When the organism is energy starved, energy can be recovered either by regenerating the high-energy phosphoanhydride bond donor (ATP in most cases) or by hydrolysis of polyP and subsequent secretion of orthophosphate to recharge the transmembrane proton gradient. Understanding how the energy state of the cell and environmental phosphate levels affect polyP metabolism is essential to improving such environmental processes as enhanced biological phosphorus removal, a treatment process that is widely used to remove excess phosphate from wastewater. Manipulation of the genes responsible for polyP metabolism can also be used to improve gene expression from phosphate-starvation promoters and to remove heavy metals from contaminated environments.     

Detection of a Rapidly Metabolizing Portion of the Membrane Cardiolipin in Haemophilus parainfluenzae

Heterogeneity in the metabolism of cardiolipin (CL) has been detected in Haemophilus parainfluenzae. Pulse-chase experiments showed that a portion of the total CL incorporated and then lost (32)P much more rapidly than the rest of the CL in the cells. The metabolism of each phosphate of the CL differed. The phosphate of the phosphatidyl glycerol (PG) portion of the CL had a more active metabolism than the phosphate of the phosphatidic acid portion of the molecule. Only a portion of the PG pool contributed to the formation of CL. Ethylenediaminetetraacetic acid inhibited the CL-specific phospholipase D in vitro and, when added to growing cells, resulted in more rapid PG metabolism, suggesting that CL hydrolysis contributed to the PG pool.     

Dependence of Streptococcus lactis phosphate transport on internal phosphate concentration and internal pH.

Uptake of phosphate by Streptococcus lactis ML3 proceeds in the absence of a proton motive force, but requires the synthesis of ATP by either arginine or lactose metabolism. The appearance of free Pi internally in arginine-metabolizing cells corresponded quantitatively with the disappearance of extracellular phosphate. Phosphate transport was essentially unidirectional, and phosphate concentration gradients of up to 10(5) could be established. Substrate specificity studies of the transport system indicated no preference for either mono- or divalent phosphate anion. The activity of the phosphate transport system was affected by the intracellular Pi concentration by a feedback inhibition mechanism. Uncouplers and ionophores which dissipate the pH gradient across the cytoplasmic membrane inhibited phosphate transport at acidic but not at alkaline pH values, indicating that transport activity is regulated by the internal proton concentration. Phosphate uptake driven by arginine metabolism increased with the intracellular pH with a pKa of 7.3. Differences in transport activity with arginine and lactose as energy sources are discussed.     

Role of phosphate in the central metabolism of two lactic acid bacteria--a comparative systems biology approach

Lactic acid-producing bacteria survive in distinct environments, but show common metabolic characteristics. Here we studied the dynamic interactions of the central metabolism in Lactococcus lactis, extensively used as a starter culture in the dairy industry, and Streptococcus pyogenes, a human pathogen. Glucose-pulse experiments and enzymatic measurements were performed to parameterize kinetic models of glycolysis. Significant improvements were made to existing kinetic models for L. lactis, which subsequently accelerated the development of the first kinetic model of S. pyogenes glycolysis. The models revealed an important role for extracellular phosphate in the regulation of central metabolism and the efficient use of glucose. Thus, phosphate, which is rarely taken into account as an independent species in models of central metabolism, should be considered more thoroughly in the analysis of metabolic systems in the future. Insufficient phosphate supply can lead to a strong inhibition of glycolysis at high glucose concentrations in both species, but this was more severe in S. pyogenes. S. pyogenes is more efficient at converting glucose to ATP, showing a higher tendency towards heterofermentative energy metabolism than L. lactis. Our comparative systems biology approach revealed that the glycolysis of L. lactis and S. pyogenes have similar characteristics, but are adapted to their individual natural habitats with respect to phosphate regulation.     

Interrelationship of polyphosphate metabolism and levorin biosynthesis in Streptomyces levoris

The effect of inorganic phosphate on biosynthesis of the polyene antibiotic levorin by Streptomyces levoris was studied. At phosphate concentration of 4.0 mM levorin biosynthesis is repressed by 90%, resulting in an increase of ATP and a condensed inorganic polyphosphates content in the producer cells. At phosphate concentration optimal for levorin production (0.04 mM) the level of intracellular ATP sharply falls by the beginning of the steady-state phase of the producer growth and that of polyphosphates decreases 3-6-fold. The inorganic phosphate exerts different effects on polyphosphate metabolism enzymes, such as polyphosphate: D-glucose-6-phosphotransferase, polyphosphate phosphohydrolase, tripolyphosphate phosphohydrolase, pyrophosphate phosphohydrolase, alkaline and acid phosphatase. The strongest effect of phosphate excess is observed in the case of polyphosphate: D-glucose-6-phosphotransferase, whose activity decreases 2-5-fold. The activity of this enzyme was shown to be correlated with the antibiotic accumulation. The data obtained are indicative of interrelationship between the polyphosphate metabolism and levorin biosynthesis.     

Engineering polyphosphate metabolism in Escherichia coli: implications for bioremediation of inorganic contaminants

Polyphosphate metabolism plays an important role in the bioremediation of phosphate contamination in municipal wastewater, and may play a key role in heavy metal tolerance and bioremediation. However, little is known about the regulation of polyphosphate metabolism in microorganisms and its role in heavy metal toxicity. We have manipulated polyphosphate metabolism in Escherichia coli by overexpressing the genes for polyphosphate kinase (ppk) and for polyphosphatase (ppx) under control of their native promoters and inducible promoters. Overexpression of ppk results in high levels of intracellular polyphosphate, improved phosphate uptake, but no increase in tolerance to heavy metals. Overexpression of both ppk and ppx results in lower levels of intracellular polyphosphate, secretion of phosphate from the cell, and increased tolerance to heavy metals. Metabolic flux analysis indicates that the cell responds to increased flux through the PPK-PPX pathway by altering flux through the TCA cycle.     

P-Nuclear Magnetic Resonance Determination of Phosphate Compartmentation in Leaves of Reproductive Soybeans (Glycine max L.) as Affected by Phosphate Nutrition

Most leaf phosphorus is remobilized to the seed during reproductive development in soybean. We determined, using ³¹P-NMR, the effect phosphorus remobilization has on vacuolar inorganic phosphate pool size in soybean (Glycine max [L.] Merr.) leaves with respect to phosphorus nutrition and plant development. Phosphate compartmentation between cytoplasmic and vacuolar pools was observed and followed in intact tissue grown hydroponically, at the R2, R4, and R6 growth stages. As phosphorus in the nutrient solution decreased from 0.45 to 0.05 millimolar, the vacuolar phosphate peak became less prominent relative to cytoplasmic phosphate and hexose monophosphate peaks. At a nutrient phosphate concentration of 0.05 millimolar, the vacuolar phosphate peak was not detectable. At higher levels of nutrient phosphate, as plants progressed from the R2 to the R6 growth stage, the vacuolar phosphate peak was the first to disappear, suggesting that storage phosphate was remobilized to a greater extent than metabolic phosphate. Under suboptimal phosphate nutrition (≤ 0.20 millimolar), the hexose monophosphate and cytoplasmic phosphate peaks declined earlier in reproductive development than when phosphate was present in optimal amounts. Under low phosphate concentrations (0.05 millimolar) cytoplasmic phosphate was greatly reduced. Carbon metabolism was coincidently disrupted under low phosphate nutrition as shown by the appearance of large, prominent starch grains in the leaves. Cytoplasmic phosphate, and leaf carbon metabolism dependent on it, are buffered by vacuolar phosphate until late stages of reproductive growth.     

Glucose Metabolism in Neisseria gonorrhoeae

The metabolism of glucose was examined in several clinical isolates of Neisseria gonorrhoeae. Radiorespirometric studies revealed that growing cells metabolized glucose by a combination on the Entner-Doudoroff and pentose phosphate pathways. A portion of the glyceraldehyde-3-phosphate formed via the Entner-Doudoroff pathway was recycled by conversion to glucose-6-phosphate. Subsequent catabolism of this glucose-6-phosphate by either the Entner-Doudoroff or pentose phosphate pathways yielded CO(2) from the original C6 of glucose. Enzyme analyses confirmed the presence of all enzymes of the Entner-Doudoroff, pentose phosphate, and Embden-Meyerhof-Parnas pathways. There was always a high specific activity of glucose-6-phosphate dehydrogenase (EC 1.1.1.49) relative to that of 6-phosphogluconate dehydrogenase (EC 1.1.1.44). The glucose-6-phosphate dehydrogenase utilized either nicotinamide adenine dinucleotide phosphate or nicotinamide adenine dinucleotide as electron acceptor. Acetate was the only detectable nongaseous end product of glucose metabolism. Following the disappearance of glucose, acetate was metabolized by the tricarboxylic acid cycle as evidenced by the preferential oxidation of [1-(14)C]acetate over that of [2-(14)C]acetate. When an aerobically grown log-phase culture was subjected to anaerobic conditions, lactate and acetate were formed from glucose. Radiorespirometric studies showed that under these conditions, glucose was dissimilated entirely by the Entner-Doudoroff pathway. Further studies determined that this anaerobic dissimilation of glucose was not growth dependent.     

Multiple regulatory roles of a novel Saccharomyces cerevisiae protein, encoded by YOL002c, in lipid and phosphate metabolism

The yeast open reading frame YOL002c encodes a putative membrane protein. This protein is evolutionarily conserved across species, including humans, although the function of each of these proteins remains unknown. YOL002c is highly expressed in yeast cells that are grown in the presence of saturated fatty acids such as myristate. Furthermore, cells in which the YOL002c gene is disrupted grow poorly on this carbon source. These mutant cells are also resistant to the polyene antibiotic, nystatin. Gene chip analysis on yol002cDelta cells revealed that a variety of genes encoding proteins involved in fatty acid metabolism and in the phosphate signaling pathway are induced in this mutant strain. In addition, our studies demonstrated that in the disruption strain acid phosphatase activity is expressed constitutively, and the cells accumulate polyphosphate to much higher levels than wild-type cells. A homologous human protein is able to partially rescue these defects in phosphate metabolism. We propose that YOL002c encodes a Saccharomyces cerevisiae protein that plays a key role in metabolic pathways that regulate lipid and phosphate metabolism.     

Overlapping binding of PhoP and AfsR to the promoter region of glnR in Streptomyces coelicolor

Growth of soil bacteria is often limited by the availability of essential nutrients such as carbon, nitrogen and phosphate. The reaction to a specific nutrient starvation triggers interconnected responses to equilibrate the metabolism. It is known that PhoP (response regulator involved in phosphate control) specifically binds to several promoters of genes involved in nitrogen metabolism which are also regulated by GlnR (regulator involved in nitrogen control). In this article we report a novel cross-talk between GlnR and the SARP-like regulator, AfsR. AfsR binds to some PhoP-regulated promoters including those of afsS (a small regulatory protein of secondary metabolism), pstS (a component of the phosphate transport system) and phoRP (encoding the two component system itself). We have characterized the regulation exerted upon the nitrogen regulator glnR gene by AfsR, using EMSA and DNase I footprinting assays as well as in vivo expression studies with ΔphoP, ΔafsR and ΔafsR-ΔphoP mutants. Both PhoP and AfsR proteins are able to bind to overlapping regions within the glnR promoter producing different effects. This work demonstrates a cross-talk of three different regulators of both primary and secondary metabolism.