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R P Newton

Publications and source records attributed to R P Newton.

At least 19 recordsLinked to original sources
PubMed2006

New insights from MALDI-ToF MS, NMR, and GC-MS: mass spectrometry techniques applied to palynology.

The present study for the first time describes the application of matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-ToF MS) to palynology. With an accessible mass range of up to about 350,000 Da at subpicomolar range, this technique is ideal for the characterisation of bio-macromolecules, such as sporopollenin, found in fossil and extant pollen and spore walls, which often can only be isolated in very small quantities. At this stage, the limited solubility of sporopollenin allows for the identification of sections of this biopolymer, but with the optimisation of MALDI-ToF matrices, further structure elucidation will become possible. Furthermore, gas chromatography-mass spectrometry (GC-MS) and (1)H nuclear magnetic resonance ((1)H NMR) spectroscopy data obtained from a number of experiments revealed that some previously reported data were misinterpreted. These results add support to the hypothesis that common plasticizers were wrongly described as sporopollenin compounds.

Butylated Hydroxytoluene↗
PubMed2005

Stainless steel electrospray probe: a dead end for phosphorylated organic compounds?

A study of the interaction of phosphorylated organic compounds with the stainless components of a liquid chromatography-electrospray ionisation-mass spectrometry system (LC-ESI-MS) was carried out to disclose a (forgotten?) likely pitfall in the LC-ESI-MS analysis of phosphorylated compounds. The retention behaviour of some representative compounds of different important classes of phosphorylated biomolecules such as nucleotides, oligonucleotides, phosphopeptides, phospholipids and phosphorylated sugars was investigated during their passage through the injector and the stainless steel electrospray capillary. It became clear that the stainless steel components within the LC-ESI-MS setup were able to retain and trap phosphorylated compounds when these compounds were introduced under acidic conditions (0.1% acetic acid). Their release from these stainless steel parts was accomplished by applying an extreme basic mobile phase (25-50% ammonium hydroxide, ca. pH 12). From the data collected one could conclude that the availability of a primary phosphate group appeared imperative but was not always sufficient to realise adsorption on a stainless surface. Furthermore, the number of phosphate moieties seemed to enhance the adsorption properties of the molecules and hence roughly correlated with the analyte fraction lost. Corrosion of the inner surface caused by the mobile phase and the electrospray process was found to be an important factor in the course of these adsorption phenomena.

Adsorption↗
PubMed2002

Screening women for postpartum depression at well baby visits: resistance encountered and recommendations.

OBJECTIVE: Postpartum major depression afflicts 10-15% of childbearing women and can have serious consequences. Unrecognized and therefore untreated episodes of postpartum major depression can predispose women to future depressive episodes, especially those related to other reproductive events. In the United States, women typically have one visit at six weeks postpartum with their obstetrician which is focused on physical recovery from delivery. Pediatricians typically see new mothers 4-6 times per year at well baby visits. Therefore, our objective is to test the utility of screening women for postpartum depression at each well baby visit over the course of the first postpartum year as compared with controls derived from clinical practice and chart review. METHOD: Subjects for this prospective study were recruited at their first well baby visit at the UCSD Primary Care Pediatric Clinic and interviewed by telephone. Subjects then were asked to complete the Edinburgh Postnatal Depression Scale (EPDS) and the Beck Depression Inventory (BDI) at intervals consistent with the timing of well baby visits. If scores on the EPDS or the BDI exceeded the thresholds (EPDS >or= 12 and BDI >or= 10) then subjects were assessed further with the Structured Clinical Interview for the Diagnostic and Statistical Manual of Mental Disorder, Fourth Edition (SCID-DSM IV). If diagnosed with postpartum major depression, subjects were referred for appropriate treatment. RESULTS: Out of 160 study packets distributed, only 7 women volunteered for the study, despite endorsement and presentation of the study by their pediatricians. Of those participants, five scored above threshold values at some point in the interval studied. DISCUSSION: The difficulty in recruitment in this study highlights some of the problems encountered in clinical practice in terms of identifying and referring women with postpartum mental illnesses. We recommend further study be focused on how to attract potentially affected women while simultaneously addressing their fears of stigma. Since resistance also was encountered in other physicians, we recommend that educational efforts be aimed at increasing knowledge and awareness of postpartum mental illnesses in both the lay and professional spheres.

Adult↗
PubMed2001

Analysis of urinary nucleosides. II. Comparison of mass spectrometric methods for the analysis of urinary nucleosides.

Qualitative and quantitative analyses of urinary nucleosides have diagnostic potential as tumour markers. We have developed separation techniques linked to mass spectrometric detection in order to overcome the problems associated with past identification and quantitation methods. The three methods of analysis utilised were: gas chromatography/mass spectrometry (GC/MS), high-performance liquid chromatography/ion-trap mass spectrometry (HPLC/ITMS) and capillary liquid chromatography/triple quadrupole mass spectrometry (CapLC/TQMS). Here we compare the relative effectiveness of each of the techniques for subsequent application in the systematic study of urinary nucleoside profiles in cancer patients. All three methods proved to be valuable techniques for such urinary nucleoside analyses, and a combination rather than one single choice is concluded as the ideal.

Chromatography, High Pressure Liquid↗
PubMed2001

Chronobiological basis of female-specific mood disorders.

Women have twice the incidence of major depression compared with men. They are prone to develop episodes of depression during times of reproductive hormonal change at puberty, with use of oral contraceptives, during the premenstrual phase of the menstrual cycle, postpartum and during the perimenopause (see review: ). describes the variety of disturbances in biological rhythms observed in mood disorders. In this report, we describe the chronobiological disturbances observed in female-specific mood disorders, namely, premenstrual dysphoric disorder, pregnancy and postpartum depression and menopause. We hypothesize that changing reproductive hormones, by affecting the synchrony or coherence between components of the circadian system, may alter amplitude or phase (timing) relationships and thereby contribute to the development of mood disorders in predisposed individuals.

Antidepressive Agents, Second-Generation↗
PubMed2000

Analysis of urinary nucleosides. I. Optimisation of high performance liquid chromatography/electrospray mass spectrometry.

In order to optimise the analysis of urinary nucleosides by high performance liquid chromatography/mass spectrometry (HPLC/MS), the HPLC separation of these compounds was performed at different 'flow rates' and 0.2mL/min was found to give both a better separation and ionisation. The ionisation conditions were optimised to give the best intensity of the molecules quasi-molecular ions. The ion distribution profile and ionisation in both positive and negative mode were examined and the detection of the protonated molecule in positive mode chosen for further analysis. The limits of detection of the method developed are reported and representative LC/MS and LC/MS/MS spectra shown. Typical urinary nucleoside chromatograms are presented.

Chromatography, High Pressure Liquid↗
PubMed2000

Development of a purification procedure for the isolation of nucleosides from urine prior to mass spectrometric analysis.

A chromatographic separation of nucleosides from urine has been developed in order to facilitate their mass spectrometric analysis for clinical diagnosis. A number of chromatographic resins were studied in order to develop an effective and efficient purification procedure. The optimized sequential protocol comprises a centrifugation, acidification and neutralization step, followed by application of an affinity chromatographic column and finally further separation on an acidic cation exchange column and a basic anion exchanger. This scheme shows effective clean-up of a standard radiolabelled nucleoside with a recovery of 92.5%, and recovery of nucleosides added to urine samples before extraction showed recoveries of 72-82%.

Acrylic Resins↗
PubMed1999

Kinetic analysis of cyclic CMP-specific and multifunctional phosphodiesterases by quantitative positive-ion fast-atom bombardment mass spectrometry.

Two enzymes, cyclic CMP-specific phosphodiesterase and multifunctional phosphodiesterase, are responsible for the hydrolysis of cytidine 3',5'-cyclic monophosphate in living cells. Quantitation of both enzymes has been carried out by positive-ion fast-atom bombardment mass spectrometric analysis of the enzyme incubates after termination of the reaction. The kinetic data obtained are in close agreement with parallel data obtained by the conventional radiometric assay. The extra facility of the mass spectrometry based assay to monitor several incubation components simultaneously has been exploited to study the concurrent hydrolysis of alternate cyclic nucleotide substrates and provides kinetic parameters of significance in interpreting substrate-enzyme interactions. This is extended by the use of collisionally-induced dissociation of the protonated molecules of the liberated products to identify the mononucleotide isomers resulting from the cyclic nucleotide hydrolysis.

2',3'-Cyclic Nucleotide 3'-Phosphodiesterase↗
PubMed1999

Studies on a haemolymph lectin isolated from Rhodnius prolixus and its interaction with Trypanosoma rangeli.

We demonstrated that in Rhodnius prolixus haemocyte monolayers, both Trypanosoma cruzi and Trypanosoma rangeli are capable of inducing haemocyte/parasite clump formation. We also purified, by one-step affinity chromatography, a haemolymph galactoside-binding lectin from R. prolixus which we believe could play an important role in the development of T. rangeli in the haemocoel of the insect vector. This lectin markedly enhanced the activation of clump formation by T. rangeli in R. prolixus haemocyte monolayers, with an increase in clump size and haemocyte aggregation. The haemolymph lectin also significantly affected the motilitity and survival of T. rangeli culture short forms, but not the long forms, when they were incubated in vitro. This molecule is also one of the few described in insects with agglutination activity independent of calcium ions. The partial N-terminal amino acid sequence of this lectin demonstrated similarity to a bacterial xylulose kinase and in preliminary experiments the purified haemolymph lectin phosphorylated a tyrosine kinase substrate in a dose-dependent manner. The possible role of this haemolymph lectin in the life cycle of T. rangeli is discussed.

Amino Acid Sequence↗
PubMed1999

Identification, purification and properties of a beta-1,3-glucan-specific lectin from the serum of the cockroach, Blaberus discoidalis which is implicated in immune defence reactions.

A lectin specific for laminarin, a beta-1,3-glucan, agglutinating baker's yeast and enhancing prophenoloxidase activation by laminarin, has been purified from the cockroach, Blaberus discoidalis, serum. Purification involved gel filtration with Bio-gel P300 and affinity chromatography on blue Sepharose CL-6B and laminarin-Sepharose 4B. The purified lectin has a molecular mass estimate of 520 kDa determined by gel filtration, and approximately 80 and 82 kDa by SDS-PAGE, under non-reducing and reducing conditions, respectively. After isoelectric focusing the lectin focused as a single band at pH 4.9. The purified lectin was stained by the periodic acid/Schiff's reagent showing that it is a glycoprotein, and was deglycosylated by endo-beta-N-acetylglu-cosaminidase F. Amino acid composition analysis showed the protein is similar to previously purified beta-1,3-glucan binding proteins from other invertebrates. In electron micrographs by negative staining, the protein formed large aggregates with 'Y'-shaped 'structural units' ca. 79 x 65 nm. Immunological tests confirmed that this lectin is not related to any other lectins previously purified from the same insect. This protein appears to be part of the hexamerin family of proteins. This is one of the first reports of a hexamerin-like molecule with lectin activity.

Agglutination Tests↗
PubMed1998

Fast-atom bombardment tandem mass spectrometry of cyclic nucleotide analogues used as site-selective activators of cyclic nucleotide-dependent protein kinases.

The mass spectrometric behaviour of six cyclic nucleotide analogues which activate cyclic AMP-dependent protein kinase was studied by positive-ion fast-atom bombardment (FAB) and collision-induced dissociation (CID) mass-analysed ion kinetic energy (MIKE) spectrometry. The compounds studied were 1,N6-ethenoadenosine-3',5'-cyclic monophosphate, (epsilon-cyclic AMP) and 2'-aza-1,N6-ethenoadenosine-3',5'-cyclic monophosphate, which each activate both isoforms of cyclic AMP-dependent protein kinase and have similar affinity for both the 'fast' and the 'slow' regulatory site of each isoform, N6-phenyl-cyclic AMP, which is selective for the 'fast' regulatory site of each isoform, and 6-chloropurine riboside-3',5'-cyclic monophosphate, 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole-3',5'-cyclic monophosphate and 8-(4-chlorophenylthio)-adenosine-3',5'-cyclic monophosphate, which are each selective for the 'slow' regulatory site and preferentially activate isoform II. The FAB- and CID/MIKE spectra of the analogues are discussed in relation to their use in studies of the regulation of protein kinase activity by quantitative FAB mass spectrometry.

Cyclic AMP↗
PubMed1997

Estimation of cytidylyl cyclase activity and monitoring of side-product formation by fast-atom bombardment mass spectrometry.

The enzyme cytidylyl cyclase catalyses the conversion of cytidine 5'-triphosphate into cytidine 3',5'-cyclic monophosphate, a third naturally occurring cyclic nucleotide currently under investigation to assign a biochemical function. Quantitation of the activity of this enzyme has been carried out by the positive-ion fast-atom bombardment mass spectrometric analysis of the enzyme incubation mixture after the reaction has been terminated. The data obtained are in good agreement with those obtained from the conventional radiometric and radioimmunoassays of the same enzyme preparations. The advantage of the mass spectrometer-based assay is the facility for multiple component monitoring. Thus, the production of the cytidine diphosphates and monophosphates, and the production of four cytidine 3',5'-cyclic monophosphate analogues as side-products, were simultaneously estimated. The identities of two of the side-products, 2'-O-glutamyl- and 2'-O-aspartyl-cytidine-3',5'-cyclic monophosphate, and of the cytidine 3',5'-cyclic monophosphate product, were confirmed by mass-analysed ion kinetic energy spectra from the collision-induced dissociation of the protonated molecules.

Animals↗
PubMed1997

Kinetic analysis and multiple component monitoring of effectors of adenylyl cyclase activity by quantitative fast-atom bombardment mass spectrometry.

The enzyme adenylyl cyclase catalyses the conversion of adenosine 5'-triphosphate (ATP) to adenosine-3',5'-cyclic monophosphate (cyclic AMP), and is an important pharmaceutical target. Quantitation of this enzyme's activity has been carried out by positive-ion fast-atom bombardment mass spectrometric analysis of the enzyme incubation mixture after the reaction has been terminated. The kinetic data obtained are in good agreement with those obtained by the conventional radiometric assay, and this mass spectrometry-based assay offers the facility to monitor the turnover of several components of the incubation simultaneously. This is utilized to study the relative efficiencies of two ATP-regenerating systems, three phosphodiesterase inhibitors and two modified substrates, and to monitor the uptake and conversion of two competing substrates, adenosine 5' triphosphate and 2'-deoxyadenosine-5-triphosphate, to cyclic AMP and to cyclic deoxyAMP, respectively.

Adenosine Triphosphate↗
PubMed1996

Analysis of 3',5'-cAMP and adenylyl cyclase activity in higher plants using polyclonal chicken egg yolk antibodies.

Polyclonal antibodies were raised in chicken against an adenosine 3',5'-monophosphate-diphtheria toxoid antigen construct. The antibodies obtained show selectivity and high affinity toward 3',5'-cyclic nucleotides while exhibiting negligible affinity for 2',3'-cyclic nucleotides and other related adenine compounds. This paper reports on the development of an immunoaffinity purification procedure allowing both adenosine 3':5'-monophosphate (3',5'-cAMP) and adenylyl cyclase activity measurement in plant tissue samples. Basically, the technique consists of sequential purification of samples on solid-phase columns, the newly developed immunoaffinity columns, and quantitative analysis in ion-suppression HPLC coupled to photo diode array detection. The described method results in a drastic reduction of processing time compared to existing procedures and combines high yields (70-80%) and thorough purification, hence significantly increasing the sensitivity of quantification of 3',5'-cAMP content in higher plant material. Used in adenylyl cyclase activity measurement it also allows for a routine positive identification of the newly formed compound, 3',5'-cAMP, a feature generally lacking in existing adenylyl cyclase assays.

Adenylyl Cyclases↗