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PubMed2005

Structural studies of glucose-6-phosphate and NADP+ binding to human glucose-6-phosphate dehydrogenase.

Human glucose-6-phosphate dehydrogenase (G6PD) is NADP(+)-dependent and catalyses the first and rate-limiting step of the pentose phosphate shunt. Binary complexes of the human deletion mutant, DeltaG6PD, with glucose-6-phosphate and NADP(+) have been crystallized and their structures solved to 2.9 and 2.5 A, respectively. The structures are compared with the previously determined structure of the Canton variant of human G6PD (G6PD(Canton)) in which NADP(+) is bound at the structural site. Substrate binding in DeltaG6PD is shown to be very similar to that described previously in Leuconostoc mesenteroides G6PD. NADP(+) binding at the coenzyme site is seen to be comparable to NADP(+) binding in L. mesenteroides G6PD, although some differences arise as a result of sequence changes. The tetramer interface varies slightly among the human G6PD complexes, suggesting flexibility in the predominantly hydrophilic dimer-dimer interactions. In both complexes, Pro172 of the conserved peptide EKPxG is in the cis conformation; it is seen to be crucial for close approach of the substrate and coenzyme during the enzymatic reaction. Structural NADP(+) binds in a very similar way in the DeltaG6PD-NADP(+) complex and in G6PD(Canton), while in the substrate complex the structural NADP(+) has low occupancy and the C-terminal tail at the structural NADP(+) site is disordered. The implications of possible interaction between the structural NADP(+) and G6P are considered.

Binding Sites↗
PubMed2001

Interdependent effects of inorganic phosphate and creatine phosphate on sarcoplasmic reticulum Ca2+ regulation in mechanically skinned rat skeletal muscle.

1. The effects of creatine phosphate (CP) and inorganic phosphate (Pi) on sarcoplasmic reticulum (SR) Ca2+ regulation were investigated in mechanically skinned muscle fibres from rat extensor digitorum longus (EDL) muscles. Changes in [Ca2+] were detected using fura-2 fluorescence, during continuous perfusion or when the solution surrounding the preparation was restricted to approximately 6 microl by stopping perfusion. 2. In solutions with 5 mM ATP and 10 mM CP, stopping the flow for 2-3 min had no effect on [Ca2+] within the bath. This suggests that SR Ca2+ uptake is balanced by an efflux under these conditions. 3. In solutions with CP, the introduction of Pi induced a small transient rise in [Ca2+], due to Ca2+ loss from the SR. Following equilibration with solutions containing Pi (> or = 5 mM), a maintained decrease in [Ca2+] occurred when the flow was stopped. This is consistent with calcium phosphate (Ca-Pi) precipitation within the SR, resulting in maintained Ca2+ uptake. 4. In the absence of CP, the [Ca2+] within the bath increased progressively when the flow was stopped. This rise in [Ca2+] was inhibited by an alternative ATP regenerating system comprising phosphoenolpyruvate (PEP) and pyruvate kinase (PK). Therefore, the loss of Ca2+ from the SR may result from local ADP accumulation and the consequent reversal of the SR Ca2+ pump. 5. In the absence of CP, the initial Ca2+ release associated with the introduction of Pi increased markedly. Following prolonged equilibration with solutions containing Pi, a rise in [Ca2+] occurred within the bath when the flow was stopped. Maintained Ca2+ uptake associated with Ca-Pi precipitation was not apparent at any level of Pi tested (1-60 mM), when CP was absent. 6. These results suggest that withdrawal of CP is associated with activation of a SR Ca2+ efflux pathway. This may involve reversal of the SR Ca2+ pump, due to local ADP accumulation. In the absence of CP, the dominant influence of Pi appears to involve further Ca2+ efflux via the SR Ca2+ pump. The possible relevance of these effects to skeletal muscle fatigue is considered.

Adenosine Triphosphate↗
PubMed1996

Investigation of a choline phosphate synthesis pathway in Streptococcus pneumoniae: evidence for choline phosphate cytidylyltransferase activity.

In this study we have demonstrated the activity of a choline phosphate cytidylyltransferase in cell free extracts of Streptococcus pneumoniae. Southern blot analysis of restricted S. pneumoniae genomic DNA probed with the gene coding for the choline phosphate cytidylyltransferase of Saccharomyces cerevisiae demonstrated that there is homology between the S. cerevisiae cct gene and genomic DNA of S. pneumoniae. We believe that this enzyme is involved in the biosynthesis of the choline containing cell wall antigens, teichoic acid and lipoteichoic acid, catalysing the activation of choline phosphate to CDP-choline which is then incorporated into the polysaccharide moiety.

Animals↗
PubMed2000

Conserved cytoplasmic motifs that distinguish sub-groups of the polyprenol phosphate:N-acetylhexosamine-1-phosphate transferase family.

WecA, MraY and WbcO are conserved members of the polyprenol phosphate:N-acetylhexosamine-1-phosphate transferase family involved in the assembly of bacterial cell walls, and catalyze reactions involving a membrane-associated polyprenol phosphate acceptor substrate and a cytoplasmically located UDP-D-amino sugar donor. MraY, WbcO and WecA purportedly utilize different UDP-sugars, although the molecular basis of this specificity is largely unknown. However, domain variations involved in specificity are predicted to occur on the cytoplasmic side of the membrane, adjacent to conserved domains involved in the mechanistic activity, and with access to the cytoplasmically located sugar nucleotides. Conserved C-terminal domains have been identified that satisfy these criteria. Topological analyses indicate that they form the highly basic, fifth cytoplasmic loop between transmembrane regions IX and X. Four diverse loops are apparent, for MraY, WecA, WbcO and RgpG, that uniquely characterize these sub-groups of the transferase family, and a correlation is evident with the known or implied UDP-sugar specificity.

Amino Acid Motifs↗
PubMed1980

Hydrolysis of pyridoxal-5'-phosphate in plasma in conditions with raised alkaline phosphate.

Hydrolysis of pyridoxal phosphate in plasma was demonstrated in patients with liver disease and other conditions with raised alkaline phosphatase, and this usually closely paralleled the alkaline phosphatase level, whether of liver or bone origin. The endogenous plasma pyridoxal phosphate was inversely related to the alkaline phosphatase, and plasma hydrolysis of pyridoxal phosphate may at least in part be responsible. Very large doses of vitamin B6 may be necessary to compensate for this hydrolysis.

Alkaline Phosphatase↗
PubMed1995

Toxic effects of butylated triphenyl phosphate-based hydraulic fluid and tricresyl phosphate in female F344 rats.

Triaryl phosphates, including tricresyl phosphate (TCP and butylated triphenyl phosphates (BTP), are used in the commercial manufacture of plastics, lubricants, and hydraulic fluids. Recent reports implicate these compounds as endocrine and reproductive toxicants that can cause cholesteryl lipidosis in adrenocortical (AC) and ovarian interstitial (OI) cells, suggesting altered metabolism of steroid hormones or cholesterol or of both. We investigated potential mechanisms of BTP and TCP toxicity to determine if there were functional abnormalities of the adrenal cortex or ovary. Groups of intact (nine or 12) and ovariectomized (six) female F344 rats, 10-12 weeks of age, received 0, 0.4 g/kg TCP, or 1.7 g/kg BTP in sesame oil vehicle or 1.7 g/kg neat BTP for 20, 40, or 60 days. All rats administered BTP and TCP developed cholesteryl lipidosis in AC and OI cells; the TCP-treated group was most severely affected. Serum concentrations of androstenedione and corticosterone were unchanged, but estradiol levels were significantly (P < or = 0.05) elevated in BTP- and TCP-treated groups (14.5 times and 37.5 times greater than controls, respectively). Vaginal cytology revealed that BTP- but not TCP-treated females had abnormal reproductive cycles that were significantly prolonged in diestrus (3 times greater than control). There were significant elevations in serum total cholesterol (TCP-treated group was 1.3 times greater than controls), low-density lipoprotein (TCP-treated group was 1.8 times greater than controls), alanine transaminase (BTP-treated group was 2 times greater than controls), and albumin (a major serum estradiol-binding protein; BTP-treated group was 4.6 g/dl vs. 3.6 g/dl for controls).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Cortex↗
PubMed1981

X-linked hypophosphatemia: effect of calcitriol on renal handling of phosphate, serum phosphate, and bone mineralization.

Eleven patients with the Mendelian phenotype of x-linked hypophosphatemia (XLH) were treated with calcitriol [1,25-(OH)2D3] and phosphate. Ten patients had received prior treatment with ergocalciferol and phosphate. Five subjects were prepubertal and six were postpubertal. Response to calcitriol was measured under nonfasting and overnight fasting protocols. Bone biopsies were obtained before and after treatment. Calcitriol (mean dose, 30 ng/kg. day) 1) raised serum phosphorus uniformly in prepubertal patients but in only two of six postpubertal subjects; 2) did not change the theoretical renal phosphate threshold in the total patient group and thus had no effect on the primary transport defect in XLH; 3) improved trabecular bone mineralization in the total patient group, as determined by bone histomorphometry. The beneficial effect on extracellular phosphorus homeostasis was attributed to improved intestinal absorption of phosphorus; improvement in bone mineralization may reflect an additional effect of 1,25-(OH)2D3 on bone itself in XLH. Mild transient hypercalcemia occurred during 0.6% of 3545 treatment days and was readily controlled by adjusting the dosage of 1,25-(OH)2D3.

Adolescent↗
PubMed1993

Particle size effect of metastable calcium phosphates on crushing strength of self-setting bioactive calcium phosphate cement.

The resistance to crushing after a self-setting bioactive calcium phosphate cement, consisting of various particle sizes of tetracalcium phosphate (TECP), dicalcium phosphate dihydrate (DCPD) and hydroxyapatite (HAP), had hardened was tested after setting at 37 degrees C, 100% RH. X-ray diffraction suggested that the cement containing fine particles of DCPD and TECP was completely transformed to HAP, but that containing larger particles was not. Since particle size of both DCPD and TECP affected the dissolution rate, the crystal growth of HAP during cement formation depended on the specific surface area (Sw) of the raw materials. The crushing strength of the cement after hardening increased with an increase of its Sw.

Bone Cements↗
PubMed2006

The effect of nitrite on aerobic phosphate uptake and denitrifying activity of phosphate-accumulating organisms.

An anaerobic/aerobic/anoxic/aerobic sequencing batch reactor (SBR) was operated with municipal wastewater to investigate the effect of nitrite on biological phosphorus removal (BPR). When nitrite accumulated, aerobic phosphate uptake activity significantly decreased and, in case of hard exposure to nitrite, BPR severely deteriorated. The interesting observation was that the relative anoxic activity of phosphate accumulating organisms (PAOs) increased after nitrite exposure. Moreover batch tests of aerobic phosphate uptake in the presence/absence of nitrite indicated that PAOs with the higher relative anoxic activity are less sensitive to nitrite exposure. From these results, we concluded that BPR is sensitive to nitrite exposure, but BPR containing PAOs with the higher relative anoxic activity is possibly more stable against nitrite than BPR containing PAOs with the lower relative anoxic activity.

Bacteria, Anaerobic↗
PubMed2006

Molecular modeling studies of the binding characteristics of phosphates to sevelamer hydrochloride--assessing a novel technique to reduce phosphates contamination.

Recent advances in the use of polymeric materials for the remediation of phosphate from aqueous systems, including biological environments, have prompted the use of computational techniques to determine which methods are feasible to model such complex systems and to model the mechanism of binding action. In particular, Sevelamer Hydrochloride (Renagel) is used as our model polymer. A relatively simple system is constructed with a dimer of Sevelamer Hydrochloride and four phosphate ions used for capture. This work reports on molecular dynamics and Monte Carlo simulations used to determine average structure, and points of intermolecular interaction, and calculate changes in volume after the successful capture of phosphate in our model. Our resulting volume changes are of the order of 20-25%, in comparison to experimental swelling measurements on similar systems, which have an average swelling of 50-60% in aqueous media.

Models, Molecular↗
PubMed1980

Biosynthesis of streptomycin. Enzymatic formation of dihydrostreptomycin 6-phosphate from dihydrostreptosyl streptidine 6-phosphate.

Incubation of O-alpha-L-dihydrostreptose (1 leads to 4) streptidine 6-phosphate (I) with a protein-free extract from Streptomyces griseus as endogenous donor and a cell-free extract from this organism led to formation of dihydrostreptomycin 6-phosphate (II). The product was identified by paper chromatography and by its degradation to dihydrostreptobiosamine (III). II was not formed when either the donor solution or the dialysed cell-free extract was omitted. The results corroborate the role of I as intermediate in streptomycin biosynthesis. The synthesis of I from dTDP-L-dihydrostreptose, streptidine 6-phosphate and a dihydrostreptosyltransferase from S. griseus has been shown previously.

Chromatography, Paper↗
PubMed1992

Identification of a phosphodiesterase that converts inositol cyclic 1:2-phosphate to inositol 2-phosphate.

Inositol 2-phosphate (Ins(2)P) has been identified in several cell types. The cellular levels of Ins(2)P appear to be directly correlated with the levels of inositol 1:2-cyclic phosphate (cIns(1:2)P) (Ross, T. S., Wang, F. P., and Majerus, P. W. (1992) J. Biol. Chem. 267, 19919-19923). In this study we have detected an enzyme in extracts from CV-1 cells and rat cerebellum that converts cIns(1:2)P to Ins(2)P and inositol 1-phosphate. This enzyme (designated cyclic hydrolase II) is not the same protein previously designated cIns(1:2)P 2-phosphohydrolase (cyclic hydrolase I). The products, heat inactivation curves, pH optima, and metal dependence of these two activities are different, and the two activities were separated by DEAE and gel filtration chromatography. Mixing of cyclic hydrolase I with cyclic hydrolase II does not effect the activity of either. The Km of the CV-1 cyclic hydrolase II for D-cIns(1:2)P is 10 microM. The enzyme is approximately 55 kDa as estimated by gel filtration analysis in the presence of sodium chloride and 120 kDa in its absence.

Animals↗
PubMed2005

Surfactant modified coir pith, an agricultural solid waste as adsorbent for phosphate removal and fertilizer carrier to control phosphate release.

The surface of coir pith, an agricultural solid waste was modified using a cationic surfactant, hexadecyltrimethylammonium bromide (HDTMA) and the modified coir pith was investigated to assess the capacity for the removal of phosphate from aqueous solution. Optimum pH for maximum phosphate adsorption was found to be 4.0. Langmuir and Freundlich isotherms were used to model the adsorption equilibrium data. Kinetic studies showed that the adsorption obeyed second order kinetics. Thermodynamic parameters were evaluated and the overall adsorption process was spontaneous and endothermic. Effect of coexisting anions has also been studied. The feasibility of using spent adsorbent as fertilizer carrier to control phosphate release was also investigated.

Adsorption↗
PubMed1992

Location of the ATP gamma-phosphate-binding sites on rat liver carbamoyl-phosphate synthetase I. Studies with the ATP analog 5'-p-fluorosulfonylbenzoyladenosine.

The gamma-phosphate subsites of the MgATP sites of rat liver carbamoyl-phosphate synthetase I have been defined by use of the ATP analog 5'-p-fluorosulfonylbenzoyladenosine (FSBA). The synthetase utilizes two molecules of MgATP, apparently in mechanistically discrete steps and at separate MgATP sites. Sequence analysis has revealed internal duplication within the synthetase molecule (Nyunoya, H., Broglie, K.E., Widgren, E.E., and Lusty, C.J. (1985) J. Biol. Chem. 260, 9346-9356) and, based on sequence similarity with other nucleotide-binding proteins, potential ATP sites have been predicted for each of the duplicated sequences. The present FSBA studies have identified four peptides within carbamoyl-phosphate synthetase I that are involved in binding MgATP. Differential effects of N-acetylglutamate, a required allosteric activator, on the interaction of FSBA with the peptides were utilized to develop the following model for two distinct MgATP sites. Peptides 631-638 and 1327-1348 (with Cys1327 and/or Cys1337 modified by FSBA) apparently form part of the binding site for the MgATP involved in bicarbonate activation. Peptides 1310-1317 and 1445-1454 (with Tyr1450 modified by FSBA) apparently form part of the binding site for the MgATP involved in phosphorylation of enzyme-bound carbamate. Each of these MgATP sites contains a peptide from one of the internal duplicated regions of the enzyme molecule, which have previously been suggested as containing MgATP sites (Nyunoya, H., Broglie, K. E., Widgren, E. E., and Lusty, C. J. (1985) J. Biol. Chem. 260, 9346-9356; Powers-Lee, S. G., and Corina, K. (1987) J. Biol. Chem. 262, 9052-9056), as well as a peptide from the flexible C-terminal region.

Adenosine↗
PubMed1989

[Kinetic properties of transketolase from the rat liver in a reaction with xylulose-5-phosphate and ribose-5-phosphate].

An analysis of steady-state kinetics of purified rat liver transketolase shows that the reaction proceeds according to a two-stroke substitution ("ping-pong") mechanism. Based on the kinetic data, a competitive relationship was shown to exist between xylulose-5-phosphate and ribose-5-phosphate for the sites of substrate binding by the substituted form of the enzyme with the formation of a non-productive abortive complex (kd = 125 microM). The values of constants of two monomolecular steps of the reaction (k2 = 42 s-1; k4 = 9.4 s-1) were determined. It was assumed that the maximum rate-limiting step of the transketolase reaction is the degradation of the substituted form of transketolase--ribose-5-phosphate complex having a rate constant of k4.

Animals↗
PubMed1987

Effects of glucagon on renal and extrarenal handling of inorganic phosphate in mice: evidence for inorganic phosphate mobilizing activity.

Glucagon administration is known to increase urinary inorganic phosphate (Pi) excretion. We have now confirmed that this effect also occurs in mice. While, at lower glucagon doses, phosphaturia was accompanied by a decrease in plasma Pi, at the highest dose of glucagon plasma Pi was not altered in spite of a massive increase in urinary Pi. This suggested that glucagon may additionally have another effect on phosphate homeostasis, i.e. of mobilizing Pi from body stores. In order to distinguish between the renal and extrarenal effects of glucagon, the animals were fed a low-phosphate diet, a procedure known to blunt the effect of several phosphaturic agents. Under these conditions, any Pi mobilized from body stores should be reflected by an increment of plasma Pi. Glucagon phosphaturia was indeed blunted under this condition. Furthermore, plasma Pi increased spontaneously by 0.82 +/- 0.14 mmol/l (mean +/- SEM) in an experimental period of 8 h during which the mice were fasted. In mice injected with zinc-protamine-glucagon subcutaneously at 4 and 16 micrograms/g of body weight, plasma Pi increased by 1.45 +/- 0.17 and 2.38 +/- 0.14 mmol/l during 8 h, respectively. Thus, it appears that exogenous glucagon is a strong Pi-mobilizing hormone. Furthermore, during the recovery phase following insulin-induced hypoglycemia, in which glucagon is thought to play a primordial role, a similar Pi mobilization to that obtained after glucagon administration was observed. Thus, since glucagon is released during fasting to maintain the homeostasis of blood glucose, it is conceivable that the mobilization of Pi induced by fasting might also have been caused by endogenous glucagon and that this hormone might be involved in Pi homeostasis.

Animals↗
PubMed1981

[Activity of renal enzymes producing ammonia from glutamine in the absence of phosphate: 2. Effect of phosphate dependent glutaminase inhibition by heating].

UNLABELLED: It is known that heating at 50 degrees C for 10 minutes inhibits phosphate dependent glutaminase (PDG) activity of renal cortex, without any effect on gamma-glutamyl transpeptidase (gamma GT) and its phosphate independent glutaminase (PIG) activity. The effect of heating on PIG and total gamma GT activities was evaluated in renal cortex homogenates of rats both in normal acid-base equilibrium and in chronic metabolic acidosis (CMA). Homogenates were incubated in a medium containing glutamine 2 mM, no phosphate, at pH 7,40. PIG activity was measured as glutamate production and total gamma GT activity as ammonia production. In normal rats PIG activity was unchanged after heating, whereas a significant decrease of total gamma GT activity was observed (p less than 0,01). CMA caused an increase in both PIG and total gamma GT activity (p less than 0,01) and these increased to a further extent after heating. In both normal and acidotic rats the glutamate production/ammonia production ratio rose to about 1. IN CONCLUSION: a) in the experimental setting used for this study PDG activity does not intervene in glutamate and ammonia production from glutamine; b) heating causes an inhibition of gamma GT activities, other than PIG, both in normal and in acidotic rats; c) in CMA heating increases PIG activity of gamma GT.

Ammonia↗