Phosphate Assay Research Articles

A sensitive enzyme-catalytic nanogold-resonance scattering spectral assay for alkaline phosphate

In pH 8.9 Tris-HCl buffer solutions, alkaline phosphatase (ALP) catalyzed the hydrolysis of ascorbic acid 2-phosphate (AAP) substrate to form ascorbic acid. Then H(3)PO(4) was added to stop the enzymatic reaction and HAuCl(4) was used to react with ascorbic acid to generate gold nanoparticles that exhibited a resonance scattering (RS) peak at 600 nm. Under the selected conditions, when the activity of ALP increased, the formed ascorbic acid and gold nanoparticles also increased. Thus, the RS intensity at 600 nm enhanced linearly. The linear range was 0.06-22 U/L, with a detection limit of 0.03 U/L. The ALP in serum was analyzed, and the results were in agreement with those of the fluorescence method.

Protein and Mineral Composition of Osteogenic Extracellular Matrix Constructs Generated with a Flow Perfusion Bioreactor

This study investigated the temporal composition of an osteogenic extracellular matrix construct generated by culturing mesenchymal stem cells in an electrospun biodegradable poly(ε-caprolactone) fiber mesh scaffold within a flow perfusion bioreactor. Constructs of different extracellular matrix maturities were analyzed for their protein and mineral composition at several culture durations by liquid chromatography-tandem mass spectrometry, scanning electron microscopy, energy-dispersive X-ray diffraction, X-ray diffraction, and calcium and phosphate assays. The analysis revealed that at short culture durations the cells deposited cellular adhesion proteins as a prerequisite protein network for further bone formation. At the later culture durations, the extracellular matrix was composed of collagen 1, hydroxyapatite, matrix remodeling proteins, and regulatory proteins. These results suggest that the later culture duration constructs would allow for improved bone regeneration due to the ability to mineralize and the capabilities for future remodeling.

Molecular Convergence of Bacterial and Eukaryotic Surface Order

The conservation of fluidity is a theme common to all cell membranes. In this study, an analysis of lipid packing was conducted via C-laurdan spectroscopy of cell surface membranes prepared from representative species of Bacteria and Eukarya. We found that despite their radical differences in composition (namely the presence and absence of membrane-rigidifying sterol) the membrane order of all taxa converges on a remarkably similar level. To understand how this similarity is constructed, we reconstituted membranes with either bacterial or eukaryotic components. We found that transmembrane segments of proteins have an important role in buffering lipid-mediated packing. This buffering ensures that sterol-free and sterol-containing membranes exhibit similar barrier properties.

Deletion of Betaine-Homocysteine S-Methyltransferase in Mice Perturbs Choline and 1-Carbon Metabolism, Resulting in Fatty Liver and Hepatocellular Carcinomas

Betaine-homocysteine S-methyltransferase (BHMT) uses betaine to catalyze the conversion of homocysteine (Hcy) to methionine. There are common genetic polymorphisms in the BHMT gene in humans that can alter its enzymatic activity. We generated the first Bhmt(-/-) mouse to model the functional effects of mutations that result in reduced BHMT activity. Deletion of Bhmt resulted in a 6-fold increase (p < 0.01) in hepatic and an 8-fold increase (p < 0.01) in plasma total Hcy concentrations. Deletion of Bhmt resulted in a 43% reduction in hepatic S-adenosylmethionine (AdoMet) (p < 0.01) and a 3-fold increase in hepatic S-adenosylhomocysteine (AdoHcy) (p < 0.01) concentrations, resulting in a 75% reduction in methylation potential (AdoMet:AdoHcy) (p < 0.01). Bhmt(-/-) mice accumulated betaine in most tissues, including a 21-fold increase in the liver concentration compared with wild type (WT) (p < 0.01). These mice had lower concentrations of choline, phosphocholine, glycerophosphocholine, phosphatidylcholine, and sphingomyelin in several tissues. At 5 weeks of age, Bhmt(-/-) mice had 36% lower total hepatic phospholipid concentrations and a 6-fold increase in hepatic triacyglycerol concentrations compared with WT (p < 0.01), which was due to a decrease in the secretion of very low density lipoproteins. At 1 year of age, 64% of Bhmt(-/-) mice had visible hepatic tumors. Histopathological analysis revealed that Bhmt(-/-) mice developed hepatocellular carcinoma or carcinoma precursors. These results indicate that BHMT has an important role in Hcy, choline, and one-carbon homeostasis. A lack of Bhmt also affects susceptibility to fatty liver and hepatocellular carcinoma. We suggest that functional polymorphisms in BHMT that significantly reduce activity may have similar effects in humans.

Synthesis and characterization of nanocrystalline calcium sulfate for use in osseous regeneration

Nanoparticles of calcium sulfate (nCS) have potential advantages as a ceramic matrix, scaffold and/or vehicle for delivering growth factors for osseous regeneration in a variety of clinical situations. The objectives of this study were to synthesize and characterize nanoparticles of hemihydrate calcium sulfate (nCS) and to develop a nCS-based system for bone regeneration. A cryo-vacuum method was used to process dihydrate CS into dihydrate nCS, which was then subjected to oven drying to produce hemihydrate. The nCS was sterilized by glow discharge treatment for use as a synthetic graft material for the treatment of bone defects. Electron microscopy showed that the nCS powder consisted of aggregates of closely arranged acicular crystals, approximately 30–80 nm in width, 400–600 nm in length and approximately 80–100 nm in diameter, providing a surface area about ten times that of conventional CS. Thorough physico-chemical characterization confirmed the composition and phase of the material. Cell viability/metabolic activity assays and alkaline phosphate assays confirmed the safety and biocompatibility of nCS. Release kinetics for adsorbed platelet-derived growth factor and bone morphogenetic protein-2 (BMP-2) suggests that nCS may serve as an appropriate vehicle for slow release delivery of these agents. The studies presented here give evidence of the advantages of nCS as a scaffold to support osteoblastic cell activity.

Spurious hypophosphatemia associated with monoclonal paraproteinemia

Hypophosphatemia is a relatively uncommon finding in clinical practice, with a prevalence of 1–5% in all hospitalized patients. However, it is an adverse prognostic marker for mortality and morbidity. Although the correlation between serum phosphate levels and symptoms is not linear,1 severe hypophosphatemia is important to recognize and treat since it can lead to rhabdomyolysis, haemolysis, respiratory failure secondary to diaphragmatic weakness and neurological abnormalities.1–3 We report a case of spurious hypophosphatemia in a patient with longstanding MGUS coincident with the onset of Waldenstrom’s macroglobulinemia due to paraprotein interference with the phosphate assay used. Clinicians should be aware of the possibility of spurious phosphate measurements in patients with paraproteinemias to avoid unnecessary investigation and intervention. A 69-year-old man with chronic kidney disease stage 4 (CKD-4) was admitted after severe hypophosphatemia was found following a routine clinic visit. He reported no new symptoms except occasional postural dizziness despite a serum phosphate level of <0.1 mmol/l. Past medical history included acute …

Effects of the pharmaceuticals gemfibrozil and diclofenac on the marine mussel (Mytilus spp.) and their comparison with standardized toxicity tests

Human pharmaceuticals, like the lipid lowering agent gemfibrozil and the non-steroidal anti-inflammatory drug diclofenac are causing environmental concern. In this study, the marine mussel (Mytilus spp.) was exposed by injection to environmentally relevant and elevated (1μg/L and 1000μg/L) concentrations of both compounds and biomarker expression was observed. Gemfibrozil exposure induced biomarkers of stress (glutathione S-transferase and metallothionein) at both concentrations 24h and 96h after exposure, respectively. Biomarkers of damage (lipid peroxidation (LPO) and DNA damage) were significantly affected, as well as the biomarker for reproduction, alkali-labile phosphate assay, indicating the potential oxidative stress and endocrine disrupting effect of gemfibrozil. Diclofenac significantly induced LPO after 96h indicating tissue damage. Additionally standard toxicity tests using the marine species Vibrio fischeri, Skeletonema costatum and Tisbe battagliai showed differences in sensitivity to both drugs in the mg/L range. Results indicate a suite of tests should be used to give accurate information for regulation.

A simple assay for 3-deoxy- d-manno-octulosonate cytidylyltransferase and its use as a pathway screen

This article describes the adaptation of a simple colorimetric assay for inorganic pyrophosphate to the enzyme 3-deoxy- d-manno-octulosonate cytidylyltransferase (CMP–KDO synthetase, KdsB, EC 2.7.7.38), a key enzyme in the biosynthesis of lipopolysaccharide (LPS) in Gram-negative organisms. This assay is particularly useful because it can be combined with the malachite green (MG) assay for inorganic phosphate to form an assay system capable of determining inorganic phosphate and inorganic pyrophosphate in the same solution (the MG/EK (eikonogen reagent) assay). This assay system has the potential for simultaneous screening of the 3-deoxy- d-manno-octulosonate (KDO) biosynthesis pathway. We tested this potential using two enzymes, KdsB and KdsC, involved in the biosynthesis and use of the key bacterial 8-carbon sugar, KDO.

Selection of alkaline phosphatase-positive induced pluripotent stem cells from human amniotic fluid-derived cells by feeder-free system

Generation of induced pluripotent stem (iPS) cells from somatic cells has been successfully achieved by ectopic expression of four transcription factors, Oct4, Sox2, Klf4 and c-Myc, also known as the Yamanaka factors. In practice, initial iPS colonies are picked based on their embryonic stem (ES) cell-like morphology, but often may go on to fail subsequent assays, such as the alkaline phosphate (AP) assay. In this study, we co-expressed through lenti-viral delivery the Yamanaka factors in amniotic fluid-derived (AF) cells. ES-like colonies were picked onto a traditional feeder layer and a high percentage AF-iPS with partial to no AP activity was found. Interestingly, we obtained an overwhelming majority of fully stained AP positive (AP+) AF-iPS colonies when colonies were first seeded on a feeder-free culture system, and then transferred to a feeder layer for expansion. Furthermore, colonies with no AP activity were not detected. This screening step decreased the variation seen between morphology and AP assay. We observed the AF-iPS colonies grown on the feeder layer with 28% AP+ colonies, 45% AP partially positive (AP+/−) colonies and 27% AP negative (AP−) colonies, while colonies screened by the feeder-free system were 84% AP+ colonies, 16% AP+/− colonies and no AP− colonies. The feeder-free screened AP+ AF-iPS colonies were also positive for pluripotent markers, OCT4, SOX2, NANOG, TRA-1-60, TRA-1-81, SSEA-3 and SSEA-4 as well as having differentiation abilities into three germ layers in vitro and in vivo. In this study, we report a simplistic, one-step method for selection of AP+ AF-iPS cells via feeder-free screening.

Antiosteoporotic compounds from seeds of Cuscuta chinensis

The seeds of Cuscuta chinensis (Tu-Si-Zi, TSZ) have long been used for the treatment of osteoporosis in China and some Asian countries. The compounds in TSZ responsible for the antiosteoporotic activity are still poorly understood. The present study was designed to investigate the osteogenic compounds in TSZ, and to evaluate their antiosteoporotic effects in osteoblastic cells. Osteoblast-like UMR-106 cells were used for bioactivity-guided isolation of the active compounds. The activity of alkaline phosphatase (ALP) in UMR-106 cells was measured by p-nitrophenyl sodium phosphate assay. The proliferation of UMR-106 cells was assayed by Alamar-Blue method. Estrogenic activity of the extracts and isolated compounds was evaluated by activation of estrogen response element (ERE) luciferase reporter expression in HeLa cells co-transfected with human estrogen receptor subtypes (ERα or ERβ) expression vectors and 5×ERE luciferase reporter plasmid. Antiestrogenic activity of the extracts and isolated compounds were evaluated by activation of activator protein-1 (AP-1) luciferase reporter expression in HeLa cells co-transfected with human estrogen receptor subtypes (ERα or ERβ) expression vectors and 6×AP-1 luciferase reporter plasmid. ALP-guided fractionation led to the isolation of five known flavonoids, quercetin, kaempferol, isorhamnetin, hyperoside and astragalin from the crude ethanolic extract of TSZ. Further study showed that kaempferol and hyperoside significantly increased the ALP activity in UMR-106 cells. Astragalin promoted the proliferation of UMR-106 cells whereas other compounds had no such effect. The isolated compounds showed estrogenic activity but quercetin, kaempferol and isorhamnetin showed more potent ERβ agonist activity. However, compared with their ER agonist activity, only quercetin and kaempferol showed potent ER antagonist activity by activating ERα/β-mediated AP-1 reporter expression. Our findings validated the clinical use of TSZ in the treatment of osteoporosis, and demonstrated that kaempferol and hyperoside are the active compounds in TSZ for the osteogenic effect.

Selective Orthosteric Free Fatty Acid Receptor 2 (FFA2) Agonists: IDENTIFICATION OF THE STRUCTURAL AND CHEMICAL REQUIREMENTS FOR SELECTIVE ACTIVATION OF FFA2 VERSUS FFA3

Free fatty acid receptor 2 (FFA2; GPR43) is a G protein-coupled seven-transmembrane receptor for short-chain fatty acids (SCFAs) that is implicated in inflammatory and metabolic disorders. The SCFA propionate has close to optimal ligand efficiency for FFA2 and can hence be considered as highly potent given its size. Propionate, however, does not discriminate between FFA2 and the closely related receptor FFA3 (GPR41). To identify FFA2-selective ligands and understand the molecular basis for FFA2 selectivity, a targeted library of small carboxylic acids was examined using holistic, label-free dynamic mass redistribution technology for primary screening and the receptor-proximal G protein [35S]guanosine 5′-(3-O-thio)triphosphate activation, inositol phosphate, and cAMP accumulation assays for hit confirmation. Structure-activity relationship analysis allowed formulation of a general rule to predict selectivity for small carboxylic acids at the orthosteric binding site where ligands with substituted sp3-hybridized α-carbons preferentially activate FFA3, whereas ligands with sp2- or sp-hybridized α-carbons prefer FFA2. The orthosteric binding mode was verified by site-directed mutagenesis: replacement of orthosteric site arginine residues by alanine in FFA2 prevented ligand binding, and molecular modeling predicted the detailed mode of binding. Based on this, selective mutation of three residues to their non-conserved counterparts in FFA3 was sufficient to transfer FFA3 selectivity to FFA2. Thus, selective activation of FFA2 via the orthosteric site is achievable with rather small ligands, a finding with significant implications for the rational design of therapeutic compounds selectively targeting the SCFA receptors.

Characterization of LipL as a Non-heme, Fe(II)-dependent α-Ketoglutarate:UMP Dioxygenase That Generates Uridine-5′-aldehyde during A-90289 Biosynthesis

Fe(II)- and α-ketoglutarate (α-KG)-dependent dioxygenases are a large and diverse superfamily of mononuclear, non-heme enzymes that perform a variety of oxidative transformations typically coupling oxidative decarboxylation of α-KG with hydroxylation of a prime substrate. The biosynthetic gene clusters for several nucleoside antibiotics that contain a modified uridine component, including the lipopeptidyl nucleoside A-90289 from Streptomyces sp. SANK 60405, have recently been reported, revealing a shared open reading frame with sequence similarity to proteins annotated as α-KG:taurine dioxygenases (TauD), a well characterized member of this dioxygenase superfamily. We now provide in vitro data to support the functional assignment of LipL, the putative TauD enzyme from the A-90289 gene cluster, as a non-heme, Fe(II)-dependent α-KG:UMP dioxygenase that produces uridine-5'-aldehyde to initiate the biosynthesis of the modified uridine component of A-90289. The activity of LipL is shown to be dependent on Fe(II), α-KG, and O(2), stimulated by ascorbic acid, and inhibited by several divalent metals. In the absence of the prime substrate UMP, LipL is able to catalyze oxidative decarboxylation of α-KG, although at a significantly reduced rate. The steady-state kinetic parameters using optimized conditions were determined to be K(m)(α-KG) = 7.5 μM, K(m)(UMP) = 14 μM, and k(cat) ≈ 80 min(-1). The discovery of this new activity not only sets the stage to explore the mechanism of LipL and related dioxygenases further but also has critical implications for delineating the biosynthetic pathway of several related nucleoside antibiotics.

Hydroxyapatite extracted from fish scale: Effects on MG63 osteoblast-like cells

In recent years, environmental and economic conditions have raised concerns about the treatment and use of bio-waste. This study analyzed hydroxyapatite extracted from fish scale (FHAP) by enzymatic hydrolysis. The structures of FHAP were characterized by Fourier transform infrared spectroscopy, particle size analyzer, scanning electron microscopy, X-ray diffraction, and energy dispersive spectrometry. The analytical results indicated that FHAP consisted of nano-sized particles with Ca/P ratio of 1.76. After FHAP particles were sintered at 800°C for 4 h, the particles showed increased porosity and surface roughness. The influence of FHAP particles on the proliferation and osteogenic differentiation of MG63 cells was also investigated. Compared with hydroxyapatite from Sigma (SHAP), FHAP significantly increased MG63 growth, whether hydroxyapatite powders were sintered or not. Under osteogenic-inductive culture condition, FHAP particles promoted osteogenic differentiation and mineralization of MG63 cells, which was confirmed by alkaline phosphate assay and von Kossa staining. This study confirms that FHAP extracted by enzymatic hydrolysis is a promising biomaterial for artificial bone fabrication.

Oral Malodorous Compound Induces Osteoclast Differentiation Without Receptor Activator of Nuclear Factor κB Ligand

Hydrogen sulfide (H(2)S), the main component of halitosis, is one of the etiologic factors for periodontitis. We recently reported that H(2)S may induce pathologic changes in rat alveolar bone. The objective of this study is to determine the effect of H(2)S on osteoclast differentiation. Murine macrophage cells RAW264 were cultured in medium lacking nuclear factor κB ligand (receptor activator of nuclear factor κB ligand) in 5% CO(2) with air at 37°C for 24 hours; then 0.05, 0.5, or 5 ng/ml H(2)S was added to the CO(2)-air mix for 4 days. The controls received the CO(2)-air mix with no H(2)S. Cell differentiation was evaluated by counting the tartrate-resistant acid-phosphatase (TRAP)-positive cells. Extracellular signaling-regulated kinase1/2 (ERK1/2) and mitogen-activated protein kinase p38 phosphorylation were examined by Western blotting. The bone-resorption activity was determined with the resorption assay of calcium phosphate. There were significantly more TRAP-positive cells at a concentration of 0.05 ng/ml H(2)S than at the other concentrations (P <0.001). Cathepsin K protein, a specific marker for osteoclasts, was expressed in the H(2)S-induced multinuclear cells. Resorption of calcium phosphate significantly increased in the H(2)S-induced TRAP-positive cells cultured on plates coated with calcium phosphate apatite (P <0.01). The phosphorylation of ERK1/2 and p38 were accelerated by H(2)S, and increased with time. PD98059 and SB203580, specific inhibitors of ERK1/2 and p38, suppressed the activation of these enzymes and osteoclast differentiation by H(2)S. Results demonstrate that H(2)S at physiologic concentrations in mouth air induces osteoclasts from RAW264 cells.

An improved malachite green assay of phosphate: Mechanism and application

The classical malachite green (MLG) assay of phosphate, which added MLG after molybdate to the acidified reaction solutions of phosphate, tolerated interference from papaverine, sildenafil, and some similar hydrophobic amines. Resonance Rayleigh scattering signals, the alleviation of interference by poly(vinyl alcohol), and the precipitation of some yellow complexes supported that the irreversible aggregation of the complexes of a hydrophobic amine of interference and phosphomolybdate reduced the amounts of phosphomolybdate accessible to MLG and caused the interference. By adding MLG before molybdate to the acidified reaction solutions of phosphate, the complexes of phosphomolybdate and MLG were preferentially formed before the complexes of phosphomolybdate and such a hydrophobic amine effectively aggregated; thereby, an improved MLG assay of phosphate with the resistance to common hydrophobic amines was developed. Using the improved MLG assay of phosphate and a phosphatase to release phosphate from AMP, a spectrometric method successfully estimated the half-inhibition concentrations of papaverine on the recombinant human cyclic nucleotide phosphodiesterase (PDE) isozyme 4 and the mixture of PDE isozymes from rabbit brain. Therefore, the improved MLG assay of phosphate was a favorable and universal technique for developing spectrometric methods for characterizing and screening inhibitors of enzymes that release phosphate during their actions.

Microtiterplate phosphate assay based on luminescence quenching of a terbium complex amenable to decay time detection

We describe a terbium-ligand complex (TbL) for a microtiterplate assay for phosphate (P) in the 0.3–100 μmol L −1 range based on luminescence quenching. As the pH optimum is at neutral pH (7.4) the probe is quenched by both, primary (H 2PO 4 −) and secondary phosphate (HPO 4 2−). The LOD is 110 nmol L −1. A Stern–Volmer study revealed that quenching is mostly static. Due to the ms-decay time of TbL, the first luminescence lifetime assay for phosphate could also be developed. The lifetime-based calibration plot is linear between 0.5 and 5 μmol L −1 of P. The effect of various surfactants on assay performance and a study on interferents are presented. The probe was successfully applied to determination of P in commercial plant fertilizers and validated against the molybdenum blue test. The probe is the most sensitive lanthanide-based probe for phosphate.

Isolated Short Stature As a Presentation of Celiac Disease in Saudi Children

The aim of this study is to assess the prevalence of isolated short stature as a clinical presentation of celiac disease in Saudi Arab children and whether some of the routine laboratory tests performed to determine the cause of short stature could suggest the diagnosis of celiac disease. A total of 91 children with short stature were included in the study. Extensive endocrine and biochemical assessments, including total protein, serum albumin, calcium phosphate and alkaline phosphatase assays; renal function tests; coagulation profile; anti-endomysial antibodies and anti-tissue transglutaminase antibody, growth hormone, thyroid stimulating hormone, free-thyroxin (FT4) assays; stool tests for giardiasis; bone age; and endoscopic intestinal biopsies, were done for all children. Ten of the 91 children had positive intestinal biopsies in the form of total villous atrophy, an increase in crypt height, and an increase in intra-epithelial lymphocyte (IEL) numbers up to >40 IEL/100 EC (Type 3C) according to the Oberhuber classification, confirming the diagnosis of celiac disease. Five children had mild villous atrophy according to this classification (Type 3A), and they were considered to have potential celiac disease. Seventy-six children had normal intestinal biopsies. Therefore, the prevalence of celiac disease among Saudi children with short stature was 10.9%, and 4.3% of the children were diagnosed as having potential celiac disease. After confirming the diagnosis of celiac disease, all children were kept on a gluten-free diet and all of them showed improvement in their growth rate. We concluded that celiac disease is a very important cause of short stature in children without gastrointestinal complaints in Saudi Arabia. We highly recommend anti-tissue transglutaminase and anti-endomysial antibody screening tests, and a small bowel biopsy to confirm the diagnosis of celiac disease irrespective of the results of the antibody assays, in children with short stature in Saudi Arabia. Once the diagnosis is confirmed, children should be kept on a gluten-free diet so they can catch up their growth early before they develop permanent short stature.

High Throughput Calorimetry for Evaluating Enzymatic Reactions Generating Phosphate

A calorimetric assay is described for the high-throughput screening of enzymes that produce inorganic phosphate. In the current example, cellobiose phosphorylase (EC 2.4.1.20) is tested for its ability to synthesise rare disaccharides. The generated phosphate is measured in a high-throughput calorimeter by coupling the reaction to pyruvate oxidase and catalase. This procedure allows for the simultaneous analysis of 48 reactions in microtiter plate format and has been validated by comparison with a colorimetric phosphate assay. The proposed assay has a coefficient of variation of 3.14% and is useful for screening enzyme libraries for enhanced activity and substrate libraries for enzyme promiscuity.

The Effects of Dietary Supplements on ATPase Activity in Ovarectomized Rats

PURPOSE: The decrease in estrogen levels following menopause has been shown to be a major contributing factor in osteoporosis. Dietary supplements have been suggested as options to counteract these effects. The risks of hypertension and other cardiovascular problems also increase dramatically after menopause. Ecto-ATPase decreases hypertension by breaking down ATP. The purpose is to determine the effects of ovarectomy on ATPase activity in rats and to evaluate the effects of dietary supplements on ATPase activity. METHODS: Female Sprague-Dawley rats (n=10) were anesthetized at 8-9 months of age (Sham). Four groups were ovarectimized and maintained with the following specifications until 19-20 months of age. OVX-control (n=9) were fed normal rat chow, OVX-PTH (n=11) were injected with parathyroid hormone for two weeks, OVX-CBD (n=11) were injected with parathyroid hormone collagen binding protein, and OVX-GT (n=9) were fed a diet of 500 mg/kg green tea polyphenols. After induction of anesthesia with pentobarbital sodium, the femoral arteries and 1A arterioles from the red gastrocnemius muscle were removed. Ecto-ATPase activity was determined using a PiBlue phosphate assay. Total protein was determined using the microBSA assay, and the enzyme activity was normalized to total protein. RESULTS: All groups showed similar ATPase activity in both the femoral arteries and 1A arterioles (G1A). For the femoral groups, means were Sham 3588.3±1883.7, OVX-control 3955.5±1511.6, OVX-PTH 3403.6±1618.6, OVX-CBD 4406.3±1280.4, and OVX-GT 4572.6±1057.3 pM phosphate. G1A group means were Sham 2602.6±2348.5, OVX-control 3357.0±1905.6, OVX-PTH 3358.4±2086.9, OVX-CBD 3887.2±1411.5, and OVX-GT 2860.3±2822.5 pM phosphate. Normalized enzyme activity for the femoral arteries was Sham 11.50±8.494, OVX-control 15.45±15.44, OVX-PTH 10.99±6.580, OVX-CBD 23.75±20.96, and OVX-GT 14.60±8.806 pM phosphate/µg protein. Normalized enzyme activity for the G1A groups was Sham 15.95±13.24, OVX-control 19.81±11.37, OVX-PTH 20.25±16.25, OVX-CBD 31.23±46.48, and OVX-GT 20.59±9.573 pM phosphate /ug protein. CONCLUSIONS: ATPase activity is not sensitive to ovarectomy or dietary manipulations focused on changing bone density. Supported by Arkansas Biosciences Institute and the NIH grant R03AG033245.

Potassium-activated GTPase Reaction in the G Protein-coupled Ferrous Iron Transporter B

FeoB is a prokaryotic membrane protein responsible for the import of ferrous iron (Fe(2+)). A defining feature of FeoB is that it includes an N-terminal 30-kDa soluble domain with GTPase activity, which is required for iron transport. However, the low intrinsic GTP hydrolysis rate of this domain appears to be too slow for FeoB either to function as a channel or to possess an active Fe(2+) membrane transport mechanism. Here, we present crystal structures of the soluble domain of FeoB from Streptococcus thermophilus in complex with GDP and with the GTP analogue derivative 2'-(or -3')-O-(N-methylanthraniloyl)-beta,gamma-imidoguanosine 5'-triphosphate (mant-GMPPNP). Unlike recent structures of the G protein domain, the mant-GMPPNP-bound structure shows clearly resolved, active conformations of the critical Switch motifs. Importantly, biochemical analyses demonstrate that the GTPase activity of FeoB is activated by K(+), which leads to a 20-fold acceleration in its hydrolysis rate. Analysis of the structure identified a conserved asparagine residue likely to be involved in K(+) coordination, and mutation of this residue abolished K(+)-dependent activation. We suggest that this, together with a second asparagine residue that we show is critical for the structure of the Switch I loop, allows the prediction of K(+)-dependent activation in G proteins. In addition, the accelerated hydrolysis rate opens up the possibility that FeoB might indeed function as an active transporter.