Search results for "Hydrogen-ion concentration"
showing 10 items of 769 documents
Mitochondrial glutathione depletion by glutamine in growing tumor cells.
2000
The effect of L-glutamine (Gln) on mitochondrial glutathione (mtGSH) levels in tumor cells was studied in vivo in Ehrlich ascites tumor (EAT)-bearing mice. Tumor growth was similar in mice fed a Gln-enriched diet (GED; where 30% of the total dietary nitrogen was from Gln) or a nutritionally complete elemental diet (SD). As compared with non-tumor-bearing mice, tumor growth caused a decrease of blood Gln levels in mice fed an SD but not in those fed a GED. Tumor cells in mice fed a GED showed higher glutaminase and lower Gln synthetase activities than did cells isolated from mice fed an SD. Cytosolic glutamate concentration was 2-fold higher in tumor cells from mice fed a GED ( approximately…
N-Propyl-N′-2-pyridylurea-modified silica as mixed-mode stationary phase with moderate weak anion exchange capacity and pH-dependent surface charge r…
2018
Herein, we present a novel silica-based stationary phase modified with N-propyl-N'-2-pyridylurea selector. Due to the weakly basic properties of the pyridine selector and the presence of residual silanols after selector immobilization, a zwitterionic surface with a pI observed at approximately pH 5.5 was measured by electrophoretic light scattering in pH-dependent ζ-potential determinations. The capability of the new N-propyl-N'-2-pyridylurea-modified silica to serve as mixed-mode stationary phase was investigated. For this purpose, it was characterized under RP and HILIC conditions using test mixtures. Subsequent classification of this stationary phase in comparison to in-house and commerc…
Determination of non-ionic and anionic surfactants in industrial products by separation on a weak ion-exchanger, derivatization and liquid chromatogr…
2013
Abstract A method for the determination of priority surfactants, including fatty alcohol ethoxylates (FAE), alkylether sulfates (AES) and linear alkylbenzene sulfonates (LAS) is described. The samples were diluted with 50% methanol at pH 4 prior to solid-phase extraction on a weak anionic exchanger (WAX). The AES and LAS surfactant classes were retained, whereas the non-ionic components, including most FAE oligomers were eluted. After washing the WAX cartridge to remove cations, the remaining hydrophobic FAE oligomers were eluted using hot 80% methanol at pH 4 (at ca. 50 °C). These two eluates were combined to constitute the non-ionic fraction. Then, AES and LAS were eluted using 80% MeOH w…
Oxygen binding properties of non-mammalian nerve globins
2006
Oxygen-binding globins occur in the nervous systems of both invertebrates and vertebrates. While the function of invertebrate nerve haemoglobins as oxygen stores that extend neural excitability under hypoxia has been convincingly demonstrated, the physiological role of vertebrate neuroglobins is less well understood. Here we provide a detailed analysis of the oxygenation characteristics of nerve haemoglobins from an annelid (Aphrodite aculeata), a nemertean (Cerebratulus lacteus) and a bivalve (Spisula solidissima) and of neuroglobin from zebrafish (Danio rerio). The functional differences have been related to haem coordination: the haem is pentacoordinate (as in human haemoglobin and myogl…
Studies on the natural hemolytic system of the annelid worm Spirographis spallanzanii viviani (Polychaeta).
1981
Abstract Hemolytic activity in the hemolymph of Spirographis spallanzanii was estabilished against Bufo, sheep, calf, rabbit, rat, human A, B, O erythrocytes. Chemico-physical treatments suggest that the hemolytic factor could be a thermo-labile protein whose activity requires calcium ions and which is active over broad pH and temperature ranges. Some of these properties and the sigmoidal curve obtained by plotting the quantity of hemolymph against the percentage of hemolysis, produce some analogies with the mammalian lytic system.
Cloning and characterization of PRA1, a gene encoding a novel pH-regulated antigen of Candida albicans.
1998
ABSTRACT Candida albicans is an opportunistic fungal pathogen of humans. The cell wall of the organism defines the interface between the pathogen and host tissues and is likely to play an essential and pivotal role in the host-pathogen interaction. The components of the cell wall critical to this interaction are undefined. Immunoscreening of a lambda expression library with sera raised against mycelial cell walls of C. albicans was used to identify genes encoding cell surface proteins. One of the positive clones represented a candidal gene that was differentially expressed in response to changes in the pH of the culture medium. Maximal expression occurred at neutral pH, with no expression d…
Beads of Acryloylated Polyaminoacidic Matrices Containing 5-Fluorouracil for Drug Delivery
2002
Spherical polymeric microparticles have been prepared by a reverse phase suspension polymerization technique. The starting polymer was alpha,beta-poly(N-2-hydroxyethyl)-DL-aspartamide (PHEA), partially derivatized with glycidylmethacrylate (GMA). PHEA-GMA copolymer (PHG) was crosslinked in the presence of N,N'-dimethylacrylamide (DMAA) or N,N'-ethylenebisacrylamide (EBA). 5-fluorouracil was incorporated into PHG-DMAA or PHG-EBA beads both during and after the crosslinking process. Swelling studies revealed a high affinity toward aqueous medium, influenced by the presence of 5-fluorouracil. The in vitro release study showed that the release rate depends on the chemical structure of the beads…
Folate-mediated targeting of polymeric conjugates of gemcitabine.
2005
The synthesis of two new macromolecular prodrugs for active tumor targeting was set up. Gemcitabine (2'-deoxy-2',2'-difluorocytidine) was conjugated to alpha,beta-poly(N-2-hydroxyethyl)-DL-aspartamide (PHEA) through succinyl or diglycolyl hydrolysable spacers. The targeting agent folic acid was attached to the macromolecular backbone through the aminocaproic spacer. The two conjugates [PHEA-(5'-succinylgemcitabine)-1'-carboxypentyl-folamide and PHEA-(5'-diglycolyl-gemcitabine)-1'-carboxypentyl-folamide], were purified and extensively characterised by spectroscopic (UV, IR and NMR) and chromatographic analyses to determine the correct chemical structure, the purity degree and the reaction yi…
Glutathione metabolism in primary astrocyte cultures: flow cytometric evidence of heterogeneous distribution of GSH content.
1993
The time-course of intracellular glutathione (GSH) values after incubation with L-buthionine-(S,R)-sulfoximine (BSO), a selective inhibitor of gamma-glutamylcysteine synthetase, showed that glutathione turns over with a half-life of 5 h. Intracellular GSH was assayed by flow cytometry using three different methods. Astrocytes showed a narrow range of cellular size but a wide range of intracellular GSH. This heterogeneity was resolved into three distinct subpopulations which represent 20%, 35% and 45% of the total astrocyte number. The less abundant subpopulation had the lower GSH content, while the most abundant was the subpopulation with the higher content. Over 95% of astrocytes were in t…
Determination of antimony in drinking waters by an inexpensive, reproducible hydride generator for atomic spectroscopy.
1991
A method for determining antimony in drinking waters is described. In order to prevent a substantial error caused by the different oxidation states of antimony, Sb(V) is reduced to Sb(III) with potassium iodide-ascorbic acid. Covalent hydride is generated with a home made device by adding NaBH4. The hydride is then atomized in a flame-heated silica tube and atomic absorption is measured spectrophotometrically. The optimal conditions for this determination are discussed and interference effects are described. Results obtained by determining linearity range (0-200 ng), detection (LOD) and quantitation (LOQ) limits (LOD = 0.347 ng/ml, LOQ = 1.158 ng/ml), precision (instrumental CV 4.08% and me…