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At least 613 records · Page 34Linked to original sources
PubMed1985

Cyclic GMP and acid production in isolated gastric cells of the rat.

Just as cAMP is regarded as an intracellular mediator of histamine, so has cGMP been connected with cholinergic stimulation of gastric acid secretion. The object of the present investigation was to study the possible role of cellular cGMP on 14C-aminopyrine uptake, an indirect measure of parietal cell H+-production, by using mixtures of isolated rat gastric cells and fractions with different parietal cell content. Cellular cAMP and cGMP. The phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) enhanced the cAMP and cGMP of gastric cells in a time- and concentration-dependent manner, by 98 and 124% (1 mmol/l) and was included in all further studies. In parietal cell enriched fractions, histamine elevated cAMP by 109% (100 mumol/l) without changing cGMP while carbachol did not influence either nucleotide. Various thiols and nitrogen compounds strongly enhanced cellular cGMP, e.g. hydroxylamine and L-cysteine (1 mmol/l) by 527 and 656%, whereas changes in cAMP were minimal. The hydroxylamine response occurred in parietal cell depleted and enriched fractions. 14C-aminopyrine (AP) uptake. IBMX alone reduced the basal AP uptake, potentiated the effect of histamine, and inhibited the effect of carbachol, which alone stimulated basal accumulation by 302%. The most efficacious stimulant of parietal cell H+-production was dibutyryl cAMP (582%, 100 mumol/l), whereas dibutyryl cGMP was without effect. However, this latter compound (1 mmol/l) reduced AP accumulation due to dibutyryl cAMP almost completely. Thiols and nitrogen compounds all more or less reduced AP uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-3-isobutylxanthine↗
PubMed1993

Influence of dietary calcium on chlordecone-induced biochemical changes in serum of rat.

Male, Sprague-Dawley rats were treated with different (1, 10, 50, and 100 ppm) concentrations of chlordecone (Cd) in calcium-sufficient (Ca-S) or calcium-deficient (Ca-D) diet for 15 days. No significant changes in serum total proteins were observed. However, serum nonprotein nitrogen compounds (urea, uric acid, and creatinine) and glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, creatine kinase, and alkaline phosphatase were significantly increased at 50 and 100 ppm of Cd. Chlordecone induced more increase in these serum components of rats fed with Ca-D as compared to Ca-S diet. Increased serum nonprotein nitrogen compounds and enzymes indicate Cd-altered glomerular and hepatic functions.

Animals↗
PubMed1982

Pleiotropic deficiency in nitrogen-uptake systems and derepression of nitrogen-catabolic enzymes in npr-1 mutants of Saccharomyces cerevisiae.

The npr-1 mutation has two types of effects in Saccharomyces cerevisiae. On one hand, several nitrogen-catabolic enzymes are derepressed in the presence of ammonia, glutamine, or asparagine, which provoke their repression in a wild-type strain. On the other hand, the activity of several ammonia-sensitive permeases is decreased (from 50-100% depending on the permease considered) in npr-1 cells, independently of the nitrogen source used for growth. Our results favour the idea that the primary effect of the npr-1 mutation is on the permeases, and that the derepression of the enzymes is a consequence of the reduced uptake rate of the repressing nitrogen compounds. Hence, the product of the npr-1 gene appears to be directly involved in the development of the activity of a set of permeases which transport nitrogen compounds and which are regulated by nitrogen effectors.

Amino Acid Transport Systems↗
PubMed2002

Nitrogen-assimilating enzymes in land plants and algae: phylogenic and physiological perspectives.

An important biochemical feature of autotrophs, land plants and algae, is their incorporation of inorganic nitrogen, nitrate and ammonium, into the carbon skeleton. Nitrate and ammonium are converted into glutamine and glutamate to produce organic nitrogen compounds, for example proteins and nucleic acids. Ammonium is not only a preferred nitrogen source but also a key metabolite, situated at the junction between carbon metabolism and nitrogen assimilation, because nitrogen compounds can choose an alternative pathway according to the stages of their growth and environmental conditions. The enzymes involved in the reactions are nitrate reductase (EC 1.6.6.1-2), nitrite reductase (EC 1.7.7.1), glutamine synthetase (EC 6.3.1.2), glutamate synthase (EC 1.4.1.13-14, 1.4.7.1), glutamate dehydrogenase (EC 1.4.1.2-4), aspartate aminotransferase (EC 2.6.1.1), asparagine synthase (EC 6.3.5.4), and phosphoenolpyruvate carboxylase (EC 4.1.1.31). Many of these enzymes exist in multiple forms in different subcellular compartments within different organs and tissues, and play sometimes overlapping and sometimes distinctive roles. Here, we summarize the biochemical characteristics and the physiological roles of these enzymes. We also analyse the molecular evolution of glutamine synthetase, glutamate synthase and glutamate dehydrogenase, and discuss the evolutionary relationships of these three enzymes.

Journal Article↗
PubMed2006

Adventures in sulfur-nitrogen chemistry.

This account reviews our efforts over the past 37 years to understand the chemistry of a select group of sulfur-nitrogen compounds including sulfinimines (N-sulfinyl imines) and N-sulfonyloxaziridines. Our early exploration of the thermal properties of sulfenamides, a class of sulfur-nitrogen compounds about which little was known, resulted in a new procedure, the silver-assisted method, for the construction of sulfenimines (N-sulfenyl imines). Selective oxidations of these compounds resulted in the production of N-sulfinyl imines (sulfinimines) and N-sulfonyloxaziridines. N-Sulfonyloxaziridines turned out to be a new class of aprotic neutral oxidizing reagents. Enantiomerically pure examples afford high ee values in the oxidation of enolates to alpha-hydroxy carbonyl compounds and in the oxidation of sulfides and selenides to sulfoxides and selenoxides. Additions of organometallic reagents to enantiomerically pure sulfinimines provide the best and most versatile method for the asymmetric construction of the carbon-nitrogen stereocenters found in many biologically active compounds. Sulfinimine-derived chiral building blocks provide efficient access to many classes of nitrogen heterocycles including aziridines, 2H-azirines, pyrrolidines, and piperidines.

Nitrogen↗
PubMed1976

Comparative pharmacologic study in vitro and in vivo with cyclophosphamide (NSC-26271), cyclophosphamide metabolites, and plain nitrogen mustard compounds.

This paper deals with the problem of the relative selectivity of the antitumor effect of cyclophosphamide (CP). CP and its metabolites are pharmacologically characterized by determining their chemical and biological activities in vitro and their pharmacotherapeutic properties in vivo. Of particular importance is the specificity of the cytotoxic activity (cytostatic units/mumol) in vitro and the margin of safety (therapeutic index) in vivo. The pharmacologic data reveal: a. Of the various metabolites of CP only 4-hydroxycyclophosphamide, the primary activation product, exerts a highly specific cytotoxic activity in vitro and has a wide margin of safety in vivo. b. The decisive step in toxication is the formation of the alkylating N,N-bis(2-chloroethyl)phosphorodiamidic acid after acrolein has been split off.

Acrolein↗
PubMed1983

Nitrogen-14 nuclear magnetic resonance spectroscopy of mammalian tissues.

The use of 14N nuclear magnetic resonance (NMR) to monitor the concentrations of nitrogenous compounds in biological tissues was investigated. 14N-NMR spectra were collected in vivo and in vitro from several tissues of the rat and rabbit. Many nitrogen-containing compounds were detected, including urea, NH+4, trimethylamines, and several amino acids. In general, the compounds detected had approximately tetrahedral symmetry about the 14N nucleus and concentrations in the millimolar range. A problem that may limit the usefulness of 14N-NMR in intact tissue is the rapid exchange of nitrogen compounds in solution with those bound to sites on macromolecules. Such interactions tend to broaden the 14N resonance signal considerably. The binding of urea to intra- and extracellular proteins is presented as a specific example of this phenomenon. A particularly interesting finding was the high concentration (approximately 90 mM) of trimethylamine compounds in the renal inner medulla. We propose that 14N-NMR is a potentially useful technique for noninvasive detection of specific nitrogen-containing compounds in intact biological tissues.

Amino Acids↗
PubMed1996

Deposition of nitrogen-containing compounds to an extensively managed grassland in central Switzerland.

During four intensive observation periods in 1992 and 1993, dry deposition of nitrogen dioxide (NO(2)) and ammonia (NH(3)), and wet deposition of nitrogen (N) were determined. The measurements were carried out in a small, extensively managed litter meadow surrounded by intensively managed agricultural land. Dry deposition of NH(3) was estimated by the gradient method, whereas eddy correlation was used for NO(2). Rates of dry deposition of total nitrate (= nitric acid (HNO(3)) + nitrate (NO(3)(-))), total nitrite (= nitrous acid (HONO) + nitrite (NO(2)(-))) and aerosol-bound ammonium (NH(4)(+)) were estimated using deposition velocities from the literature and measured concentrations. Both wet N deposition and the vertical NH(3) gradient were measured on a weekly basis during one year. Dry deposition was between 15 and 25 kg N ha(-1) y(-1), and net wet deposition was about 9.0 kg N ha(-1) y(-1). Daily average NO(2) deposition velocity varied from 0.11 to 0.24 cm s(-1). Deposition velocity of NH(3), was between 0.13 and 1.4 cm s(-1), and a compensation point between 3 and 6 ppbV NH(3) (ppb = 10(-9)) was found. Between 60 and 70% of dry deposition originated from NH(3) emitted by farms in the neighbourhood. It is concluded that total N deposition is exceeding the critical load for litter meadows, is highly correlated to local NH(3) emissions, and that NH(3) is of utmost importance with respect to possible strategies to reduce N deposition in rural regions.

Journal Article↗
PubMed2001

TRANSPORTERS RESPONSIBLE FOR THE UPTAKE AND PARTITIONING OF NITROGENOUS SOLUTES.

The acquisition and allocation of nitrogenous compounds are essential processes in plant growth and development. The huge economic and environmental costs resulting from the application of nitrogen fertilizers make this topic very important. A diverse array of transporters varying in their expression pattern and also in their affinity, specificity, and capacity for nitrogenous compounds has been identified. Now the future challenge is to define their individual contribution to nitrogen nutrition and signalling processes. Here we have reviewed recent advances in the identification and molecular characterization of these transporters, concentrating on mechanisms existing at the plasma membrane. The review focuses on nitrate, ammonium, and amino acid transporter familes, but we also briefly describe what is known at the molecular level about peptide transporters and a recently identified family implicated in the transport of purines and their derivatives.

Journal Article↗
PubMed2002

An efficient nitration of light alkanes and the alkyl side-chain of aromatic compounds with nitrogen dioxide and nitric acid catalyzed by N-hydroxyphthalimide.

Nitration of light alkanes and the alkyl side-chain of aromatic compounds with NO(2) and HNO(3) was successfully achieved by the use of N-hydroxyphthalimide (NHPI) as a catalyst under relatively mild conditions. For example, the nitration of propane with NO(2) catalyzed by NHPI at 100 degrees C for 14 h gave 2-nitropropane in good yield without formation of 1-nitropropane and cleaved products such as nitroethane and nitromethane. Various aliphatic nitroalkanes, which are difficult to prepare by conventional methods, could be selectively obtained by means of the present methodology by using NHPI as the key catalyst. In addition, the side-chain nitration of alkylbenzenes such as toluene was selectively carried out to lead to alpha-nitrotoluene without the ring nitration. The present reaction provides an efficient selective method for the nitration of light alkanes and alkylbenzenes, which has been very difficult to carry out so far.

Journal Article↗
PubMed2000

Toward a reverse osmosis membrane system for recycling space mission wastewater.

Essential to extended human exploration and utilization of space is providing a clean supply of potable water as well as water for washing. Recycling of space mission wastewater is necessary for long-term space missions due to the limited capacity of water storage. In this study, initial measurements toward a wastewater reclamation system that provides a clean water supply using reverse osmosis (RO) membranes have been made using stirred cell filtration experiments. Low-pressure reverse osmosis (LPRO) membranes were used to obtain high flux of permeate as well as high rejection. Detergent removal was above 99%, and dissolved salt removal was above 90% in single-pass treatment, while total organic carbon (TOC) removal was nearly 80%. Most problematic is nitrogen rejection, which was 74% at best. Comparison of feed water before and after urea hydrolysis shows that the rejection of nitrogen compounds can be increased to 95% by allowing urea hydrolysis to occur. The removal efficiency for nitrogen compounds was also improved by increasing the shear rate near membrane surface. As a result, the product water in two passes could meet the hygiene water requirements for human space missions, and the product water in three passes could meet potable water regulations with overall recovery of 77%. This study also suggests that dynamic rotating membrane filtration, which can produce a high shear rate, will be useful to increase the system recovery as well as pollutant rejection. Grant numbers: NAG9-1053

Ecological Systems, Closed↗
PubMed1998

Microbial denitrogenation of fossil fuels.

The microbial degradation of nitrogen compounds from fossil fuels is important because of the contribution these contaminants make to the formation of nitrogen oxides (NOx) and hence to air pollution and acid rain. They also contribute to catalyst poisoning during the refining of crude oil, thus reducing process yields. We review the current status of microbial degradation of aromatic nitrogen compounds and discuss the potential of microbial processes to alleviate these problems.

Acid Rain↗
PubMed2006

Modification of glass fibers to improve reinforcement: a plasma polymerization technique.

OBJECTIVES: This study evaluates the effect of plasma treated E-glass fiber to improve the mechanical properties of acrylic resin denture base material, polymethylmethacrlyate (PMMA). Plasma surface treatment of fibers is used as reinforcement in composite materials to modify the chemical and physical properties of their surfaces with tailored fiber-matrix bonding strength. METHODS: Three different types of monomer 2-hydroxyethyl methacrylate (HEMA), triethyleneglycoldimethylether (TEGDME) and ethylenediamine (EDA) were used in the plasma polymerization modification of glass fibers. A radiofrequency generator was used to sustain plasma in a glass vacuum chamber. Glass fibers were modified at the same glow-discharge power of 25 W and exposure time of 30 min for each monomer. Fibers were incorporated into the acrylic with 1% (w/w) loading except control group. Specimens were prepared using a standard mold of 3 cmx0.5 cmx0.8 cm in dimension with eight specimens in each group. Samples were subjected to a flexural strength test set up at a crosshead speed of 5mm/min. Scanning electron microscopy (SEM) was used to examine the microstructure and X-ray photoelectron spectroscopy (XPS) was used for chemical analysis of the surface. RESULTS: Data were analyzed by means of ANOVA and Duncan's tests. Test results revealed that fiber reinforcement had a significant effect on the flexural strength of the specimens (p<0.05). Among the fiber reinforced groups, plasma treatment with EDA monomer resulted in the most significant increase in flexural strength values (p<0.05). XPS results have shown an increasing number of nitrogenous compounds in EDA treated fibers. The chemical structure of the surface, especially with the increase in nitrogenous compounds could give an idea for the amine film deposition and SEM figures showed an increase in surface roughness. SIGNIFICANCE: The results showed that plasma treatment with EDA monomer was an effective alternative method of increasing the flexural strength of PMMA based denture base polymers through fiber reinforcement.

Analysis of Variance↗