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At least 217 records · Page 12Linked to original sources
PubMed1973

The interrelationship of the concentration of hydrogen ions, bicarbonate ions, carbon dioxide and calcium ions in the regulation of renal gluconeogenesis in the rat.

1. The interrelationship of acidosis and Ca(2+) on the stimulation of gluconeogenesis by rat kidney-cortex slices was studied. 2. Ca(2+) stimulated gluconeogenesis from glutamine, glutamate, 2-oxoglutarate, succinate, malate, pyruvate, lactate and fructose, but not from galactose. 3. The [Ca(2+)] needed for optimum gluconeogenesis was about 2mm, but at this concentration, acidosis, produced in vitro by a decrease of [HCO(3) (-)] in the medium at constant pCO(2) or by an increase in pCO(2) at constant [HCO(3) (-)], did not stimulate gluconeogenesis. 4. In the absence of Ca(2+), acidosis (low [HCO(3) (-)]) stimulated gluconeogenesis from glutamine, glutamate, 2-oxoglutarate, succinate, malate, pyruvate and lactate but not from fructose or galactose. With succinate as substrate, the stimulatory effect of acidosis (low [HCO(3) (-)]) disappeared at Ca(2+) concentrations above 1.0mm. 5. The [HCO(3) (-)] was the most important determinant of the acidosis effect since a decrease of pH caused by an increase in pCO(2) did not uniformly stimulate gluconeogenesis, whereas a decrease in [HCO(3) (-)] without a change in pH consistently stimulated glucose formation in a way similar to the stimulation produced by acidosis (low [HCO(3) (-)]) in the absence of Ca(2+). 6. Acidosis in vitro inhibited the rate of decrease of activity of phosphoenolpyruvate carboxylase in slices, and Ca(2+) caused an increase in the activity of fructose 1-phosphate aldolase. 7. Respiratory acidosis in vitro caused an increase in the activity of phosphoenolpyruvate carboxylase in kidney cortex and an increase in gluconeogenesis from glutamine. 8. Possible points of interaction between Ca(2+), H(+) and HCO(3) (-) with the gluconeogenic sequence are discussed.

Acidosis↗
PubMed2002

Isomerization and dissociation of C2X5+ and C2X4+* ions (X = Cl, F) from chlorofluoroethanes in an ion trap mass spectrometer.

The collision-induced dissociation of C(2)X(5)(+) (C(2)Cl(2)F(3)(+), C(2)Cl(3)F(2)(+) and C(2)Cl(4)F(+)) and C(2)X(4)(+.) ions (C(2)ClF(3)(+*), C(2)Cl(2)F(2)(+*), and C(2)ClF(3)(+*)) derived from three chlorofluoroethanes (the isomeric 1,1,1- and 1,1,2-trichlorotrifluoroethane and 1,1,1,2-tetrachlorodifluoroethane) was investigated by means of multi-stage mass spectrometric (MS(n)) experiments in an ion trap mass spectrometer. The observation of a common dissociation pattern for ions of any given elemental composition suggests that the experiments could not differentiate isomeric C(2)X(5)(+) ions formed from different neutral precursors and originally having different structures. For any given elemental composition, a common dissociation pattern was observed, suggesting that energy barriers for isomer interconversion are lower than for dissociation. For ions containing two or more fluorine atoms, the major (in some cases unique) dissociation involves C-C cleavage to form CX(3)(+) and CF(2). Energetically, CF(2) loss is always the most favorable reaction; mechanistically it implies, at least in some cases, rearrangement via halogen transfer from one carbon to the other (for example, in the case of the C(2)Cl(2)F(3)(+) species derived from 1,1,1-trichlorotrifluoroethane, which should have initially the Cl(2)C(+)-CF(3) structure). Similar behavior was observed with C(2)X(4)(+*) ions produced both from the three chlorofluoroethanes and from model alkenes (trifluorochloroethene and tetrachloroethene). The dissociation behavior of these C(2)X(4)(+*) species is characteristic of the ion composition, with no memory of the original neutral precursor structure. Specifically, C(2)Cl(2)F(2)(+*) ions dissociate uniquely via loss of CF(2), C(2)ClF(3)(+*) ions eliminate preferentially CF, with CF(2) loss being only a minor reaction, whereas C(2)Cl(3)F(+*) and C(2)Cl(4)(+*) dissociate exclusively via Cl elimination.

Journal Article↗
PubMed1982

Effects of variation of ion and methylation of carrier on the rate constants of macrotetralide-mediated ion transport in lipid bilayers.

The effects of methylation on the rate constants of carrier-mediated ion transport have been studied on monooleindecane bilayers with K+, Rb+, NH4+, and Tl+ ions, using the series of homologue carriers, nonactin, monactin, dinactin, trinactin, and tetranactin, each member of the series differing from the previous one by only one methyl group. Measurements of the amplitude and time constant of the current relaxation after a voltage jump over a large domain of voltage and permeant ion concentration, together with a computer curve-fitting procedure, have allowed us, without the help of steady-state current-voltage data, to deduce and compare the values of the various rate constants for ion transport: formation (kRi) and dissociation (kDi) of the ion-carrier complex at the interface, translocation across the membrane interior of the carrier (ks) and the complex (kis). With the additional information from steady-state low-voltage conductance measurements, we have obtained the value of the aqueous phase-membrane and torus-membrane partition coefficient of the carrier (gammas and gammas). From nonactin to tetranactin with the NH4+ ion, kis, and gammas are found to increase by factors of 5 and 3, respectively, kDi and gammas to decrease respectively by factors 8 and 2, while kRi and ks are practically invariant. Nearly identical results are found for K+, Rb+, and Tl+ ions. kRi, ks and kis are quite invariant from one ion to the other except for Tl+ were kRi is about five times larger. On the other hand, kDi depends strongly on the ion, indicating that dissociation is the determining step of the ionic selectivity of a given carrier. The systematic variations in the values of the rate constants with increasing methylation are interpreted in terms of modification of energy barriers induced by the carrier increasing size. Within this framework, we have been able to establish and verify a fundamental relationship between the variations of kis and kDi with methylation.

Anti-Bacterial Agents↗
PubMed2005

Fragmentation of negative ions from carbohydrates: part 1. Use of nitrate and other anionic adducts for the production of negative ion electrospray spectra from N-linked carbohydrates.

Negative ion spectra of N-linked glycans were produced by electrospray from a dilute solution of the glycans and various salts in methanol:water using a Waters-Micromass Q-TOF Ultima Global tandem quadrupole/time-of-flight (Q-TOF) mass spectrometer. Stable anionic adducts were formed with chloride, bromide, iodide, nitrate, sulphate, and phosphate. Unstable adducts that fragmented by a cross-ring cleavage of the reducing N-acetylglucosamine (GlcNAc) residue, were formed with fluoride, nitride, sulphide, carbonate, bicarbonate, hydroxide, and acetate. Nitrate adducts prepared from ammonium nitrate produced the most satisfactory spectra as they were relatively free from in-source fragmentation products and gave signals that were about ten times as strong as those from corresponding [M - H]- ions prepared from solutions containing ammonium hydroxide. Detection limits were in the region of 20 fmol. Neutral glycans gave both singly- and doubly-charged ions with the larger glycans preferring the formation of doubly-charged ions. Acidic glycans with several acidic groups gave ions in higher charge states as the result of ionization of the anionic groups. Low energy collision-induced decomposition (CID) spectra of the singly-charged ions were dominated by cross-ring and C-type fragments, unlike the corresponding spectra of the positive ions that contained mainly B- and Y-type glycosidic fragments. Formation of these ions could be rationalized by proton abstraction from various hydroxy groups by an initially-formed anionic adduct. Prominent glycosidic and cross-ring cleavage ions defined structural features such as the specific composition of each of the two antennae, presence of a bisecting GlcNAc residue and location of fucose residues, details that were difficult to determine by conventional techniques. Acidic glycans fragmented differently on account of charge localization on the acid functions rather than the hydroxy groups.

Anions↗