Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0847097 (acidity)
 15,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The role of acidity in determining and restricting plant distribution and performance is discussed. In soils especially, a key effect of H+ ion concentration is on the solubility of potentially toxic heavy metals such as aluminum, managenese, zinc, iron, copper, and nickel. Al has been reported from many studies since the 1920's as the key determining toxic factor in acid soils. Some acid-tolerant species have been shown to be especially tolerant of Al, and mechanisms of tolerance have been suggested. Mn is also a commonly toxic factor at soil pH less than 5.0. Calcium has been shown to alleviate Mn toxicity. Low pH soils are also generally low in Ca, K, Na, and P; all essential major elements for plant growth. In lakes and marine situations acidic waters are uncommon as the waters are buffered. Calcium is again ameliorative of metal toxicities. The pH, redox, and valency state are critical in determining nutrient availability and metal speciation. Recent increases in the H+ ion content of precipitation have caused increased acidities of freshwater lakes in Scandinavia and eastern North America, which have depleted biota, including fish populations.
 ...
PMID:Effect of H+ ion activity and Ca2+ on the toxicity of metals in the environment. 3 Dec 77

Orthodontic archwires (equiatomic TiNi alloy) of both used (4 weeks) and unused conditions were microanalyzed by optical and scanning electron microscopes, energy dispersive X-ray spectroscopy, and electron diffraction to characterize the surface layers. They were also subjected to immersion and polarization corrosion tests in a 0.9% NaCl aqueous solution. Based on results obtained from these analytical and experimental studies, surfaces of TiNi archwires were further electrochemically treated to etch away nickel selectively and reform the surface morphology to uniform and porous surface layers. Main conclusions were: (a) surface layers of used archwires were covered contaminants causing the discoloration, and the contaminants were identified as mainly KCl crystals, (b) surfaces of both used and unused wires were observed to be irregular features characterized by lengthy island-like structures, where nickel was selectively dissolved, (c) corrosion tests in a 0.9% NaCl aqueous solution in immersion and polarization methods indicated that by increasing temperature from 3 degrees to 60 degrees C and acidity from pH 11 to pH 3, calculated corrosion rates increased, and (d) surface layers of TiNi archwires can be electrochemically modified to selectively etch nickel away, leaving a Ti-enriched surface layer and forming a uniformly distributed porous surface that may reduce the coefficient of friction against the orthodontic brackets.
 ...
PMID:Microanalytical characterization and surface modification of TiNi orthodontic archwires. 147 8

Changes in the mechanical properties of a nickel-titanium orthodontic alloy, nitinol (0.016-inch arch wires), were studied in a simulated oral environment across time, at various levels of acidity, and at different amounts of static deflection. Significant decreases in specific mechanical properties were observed in these incubated wires compared with a group kept dry and unstressed. Ultimate tensile strain, modulus of elasticity, and 0.2% yield strength each decreased. Acidity (pH 3 to 7) and amount of deflection (0 to 4 mm in a 10-mm span) did not affect the wire, but there was a significant, monotonic decrease in yield strength with time in the simulated oral environment. By 4 months this measure of susceptibility to permanent deformation increased by 15%. Consequently, long-term use (or reuse) of a nitinol wire may be associated with a modest, but statistically significant, degradation in performance, notably in the limit of the wire's elasticity.
 ...
PMID:Nitinol arch wire in a simulated oral environment: changes in mechanical properties. 316 85

The acidity constant of protonated 2-[bis(2-hydroxyethyl)amino]-2(hydroxymethyl)-1,3-propanediol (Bistris) has been measured. The influence of hydroxo groups on the basicity of Bistris and related bases is discussed. The interaction of Bistris with the metal ions (M2+) Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Pb2+ was studied by potentiometry and spectrophotometry in aqueous solution (I = 1.0 M, KNO3; 25 degrees C) and the stability constants of the M(Bistris)2+ complexes were determined. Unexpectedly Ca(Bistris)2+ is the most stable among the alkaline earth ion complexes (log KCaCa(Bistris) = 2.25; the corresponding values for the Mg2+, Sr2+ and Ba2+ complexes are 0.34, 1.44 and 0.85, respectively). The ions of the 3d series follow the Irving-Williams sequence: log KMnMn(Bistris) = 0.70, for Cu2+, 5.27 and Zn2+ 2.38. Ternary complexes containing ATP4- as a second ligand were also investigated: the values for delta log KM (= log KM(ATP)M(ATP)(Bistris) -log KMM(Bistris) are in general negative (e.g. delta log KCa = -0.40 or delta log KCu = -1.65), thus indicating that the interaction of Bistris with M(ATP)2- is somewhat less pronounced tan with M2+. However, even in mixed-ligand systems, complex formation may still be considerable, hence great reservations should be exercised in employing Bistris as a buffer in systems containing metal ions. Moreover, in several cases delta log KM is relatively high [for Mg2+-ATP4- -Bistris even positive], indicating some cooperativity between the coordinated ligands, possibly hydrogen-bond formation. Distributions of the complexes in dependence on pH are given, and the structures of the binary M(Bistris)2+ and the ternary M(ATP) (Bistris)2- complexes are discussed. The participation of Bistris hydroxo groups in complex formation is evident.
 ...
PMID:Metal ion/buffer interactions. Stability of binary and ternary complexes containing 2-[bis(2-hydroxyethyl)amino]-2(hydroxymethyl)-1,3-propanediol (Bistris) and adenosine 5'-triphosphate (ATP). 739 53

This study concerns the inhibitory effects of acid pH and nickel on growth, nutrient (NO3- and NH4+) uptake, carbon fixation, O2 evolution, electron transport chain and enzyme (nitrate reductase and ATPase) activities of acid tolerant and wild-type strains of Chlorella vulgaris. Though a general reduction in all these variables was noticed with decreasing pH, the tolerant strain was found to be metabolically more active than the wild-type. A reduced cation (NH4+, Na+, K+ and Ca2+) uptake, coupled with a facilitated influx of anions (NH4+, PO4(3-) and HCO3-), suggested the development of a positive membrane potential in acid tolerant Chlorella. Nevertheless, a tremendous increase in ATPase activity at decreasing pH revealed the involvement of superactive ATPase in exporting H+ ions and keeping the internal pH neutral. A difference in Na+ and K+ efflux of the two strains at decreasing pH suggests there is a difference in membrane permeability. The low toxicity of Ni in the acid tolerant strain may be due to the low Ni uptake brought about by a change in membrane potential as well as in permeability. Hence, the development of superactive ATPase and a change in both membrane potential and permeability not only offers protection against acidity, but also co-tolerance to metals.
 ...
PMID:Effect of nickel on certain physiological and biochemical behaviors of an acid tolerant Chlorella vulgaris. 814 21

Epidemiologic studies have reported causal relationships between exposures to high concentrations of ambient air particles (AAP) and increased morbidity in individuals with underlying respiratory problems. Polymorphonuclear leukocytes (PMN) are frequently present in the airways of individuals exposed to particles. Upon particulate stimulation the PMN may release reactive oxygen species (ROS), which can result in tissue damage and injury. In this study a wide range of AAP samples from divergent sources (1, natural dust; 2, oil fly ash; 2, coal fly ash; 5, ambient air; and 1, carbon black) were analyzed for elemental content and solubility in relation to their ability to generate ROS. Elemental analyses were carried out in AAP and dH(2)O-washed AAP using energy dispersive x-ray fluorescence (XRF). Percent of sample mass accounted for by XRF-detectable elements was 1.2% (carbon black); 22-29% (natural dust and ambient air particles); 13-22% (oil fly ash particles); 28-49% (coal fly ash particles). The major proportion of elements in most of these particles were aluminosilicates and insoluble iron, except oil-derived fly ash particles in which soluble vanadium and nickel were in highest concentrations, consistent with particle acidity as measured in the supernatants. Human blood-derived monocytes and PMN were exposed to AAP and dH(2)O-washed particles, and generation of ROS was determined using luminol-enhanced chemiluminescence (LCL) assay. All the particles induced chemiluminescence response in the cells, except carbon black. The oxidant response of monocytes induced by AAP (with the exception of oil fly ash particles) was less than the response elicited by PMN. The LCL response of PMN in general increased with all washed particles, with oil fly ash (OFA) and one urban air particle showing statistically significant (p < 0. 05) differences between dH(2)O-washed and unwashed particles. The LCL activity in PMN induced by both particles and dH(2)O-washed particles was significantly correlated with the insoluble Si, Fe, Mn, Ti, and Co content of particles (p < 0.05). No relationship between LCL activity in PMN and soluble transition metals such as V, Cr, Ni, and Cu was noted. Pretreatment of the particles with a metal ion-chelator, deferoxamine, did not affect LCL in PMN, suggesting that metal ions are not related to the induction of LCL in PMN. Particulate S content and acidity of the particles as measured in the supernatants did not relate to LCL activity in PMN. These results point to the possibility that the insoluble constituents of the particles are related to LCL in PMN. Since some of these dusts are capable of depositing in the lungs and can cause infiltration of PMN, the ability to activate those cells may contribute to particulate toxicity.
 ...
PMID:Ambient air particles: effects on cellular oxidant radical generation in relation to particulate elemental chemistry. 1040 23

The role of metal ions in the T- to R-allosteric transition is ascertained from the investigation of the T- to R-allosteric transition of transition metal ions substituted-insulin hexamers, as well as from the kinetics of their dissociation. These studies establish that ligand field stabilization energy (LFSE), coordination geometry preference, and the Lewis acidity of the metal ion in the zinc sites modulate the T- to R-state transition. (1)H NMR, (113)Cd NMR, and UV-vis measurements demonstrate that, under suitable conditions, Fe2+/3+, Ni2+, and Cd2+ bind insulin to form stable hexamers, which are allosteric species. (1)H NMR R-state signatures are elicited by addition of phenol alone in the case of Ni(II)- and Cd(II)-substituted insulin hexamers. The Fe(II)-substituted insulin hexamer is converted to the ferric analogue upon addition of phenol. For the Fe(III)-substituted insulin hexamer, appearance of (1)H NMR R-state signatures requires, additionally to phenol, ligands containing a nitrogen that can donate a lone pair of electrons. This is consistent with stabilization of the R-state by heterotropic interactions between the phenol-binding pocket and ligand binding to Fe(III) in the zinc site. UV-vis measurements indicate that the (1)H NMR detected changes in the conformation of the Fe(III)-insulin hexamer are accompanied by a change in the electronic structure of the iron site. Kinetic measurements of the dissociation of the hexamers provide evidence for the modulation of the stability of the hexamer by ligand field stabilization effects. These kinetic studies also demonstrate that the T- to R-state transition in the insulin hexamer is governed by coordination geometry preference of the metal ion in the zinc site and the compatibility between Lewis acidity of the metal ion in the zinc site and the Lewis basicity of the exogenous ligands. Evidence for the alteration of the calcium site has been obtained from (113)Cd NMR measurements. This finding adds to the number of known conformational changes that occur during the T- to R-transition and is an important consideration in the formulation of allosteric mechanisms of the insulin hexamer.
 ...
PMID:Role of metal ions in the T- to R-allosteric transition in the insulin hexamer. 1052 Dec 51

Klebsiella aerogenes urease uses a dinuclear nickel active site to catalyze urea hydrolysis at >10(14)-fold the spontaneous rate. To better define the enzyme mechanism, we examined the kinetics and structures for a suite of site-directed variants involving four residues at the active site: His320, His219, Asp221, and Arg336. Compared to wild-type urease, the H320A, H320N, and H320Q variants exhibit similar approximately 10(-)(5)-fold deficiencies in rates, modest K(m) changes, and disorders in the peptide flap covering their active sites. The pH profiles for these mutant enzymes are anomalous with optima near 6 and shoulders that extend to pH 9. H219A urease exhibits 10(3)-fold increased K(m) over that of native enzyme, whereas the increase is less marked ( approximately 10(2)-fold) in the H219N and H219Q variants that retain hydrogen bonding capability. Structures for these variants show clearly resolved active site water molecules covered by well-ordered peptide flaps. Whereas the D221N variant is only moderately affected compared to wild-type enzyme, D221A urease possesses low activity ( approximately 10(-)(3) that of native enzyme), a small increase in K(m), and a pH 5 optimum. The crystal structure for D221A urease is reminiscent of the His320 variants. The R336Q enzyme has a approximately 10(-)(4)-fold decreased catalytic rate with near-normal pH dependence and an unaffected K(m). Phenylglyoxal inactivates the R336Q variant at over half the rate observed for native enzyme, demonstrating that modification of non-active-site arginines can eliminate activity, perhaps by affecting the peptide flap. Our data favor a mechanism in which His219 helps to polarize the substrate carbonyl group, a metal-bound terminal hydroxide or bridging oxo-dianion attacks urea to form a tetrahedral intermediate, and protonation occurs via the general acid His320 with Asp221 and Arg336 orienting and influencing the acidity of this residue. Furthermore, we conclude that the simple bell-shaped pH dependence of k(cat) and k(cat)/K(m) for the native enzyme masks a more complex underlying pH dependence involving at least four pK(a)s.
 ...
PMID:Kinetic and structural characterization of urease active site variants. 1091 64

This paper describes the condition of forest ecosystems subjected to smelter pollution in the Kola peninsula. This assessment is based on the parameters of the biogeochemical cycle. The defoliation index was used to delimit three basic forest states: background, defoliating, sparse. Close to the smelter, due to expansion of the area not covered by vegetation, a fourth type of state, so-called "industrial deserts", has been observed. The concentrations of sulphur, copper and nickel in the precipitation in the forests generally declined with distance from the smelter. The defoliating forests are noted for the highest Ca, Mg, K concentrations in the summer precipitation. In sparse forests and industrial deserts a decrease in the Ca, Mg, K concentrations in the summer precipitation in comparison with the defoliating forests, despite the particle emissions, could be attributed to the reduction in forest biomass. The higher levels of soil and soil leachate carbon and acidity in the defoliating forests was due to higher litterfall and to the higher dissolution of fulvic acids by the acidic precipitation. This increase in organic matter levels affects soil cation exchange capacity and cation saturation. The pine trees demonstrated significant changes in the uptake of elements in all types of forests under pollution. Elevated levels of S, Ni, Cu and K and reduced levels of Mg, Mn and Zn were found in the needles of different age classes.
 ...
PMID:Assessment of environmental impact zones in the Kola Peninsula forest ecosystems. 1114 14

A silica gel based sorbent containing rhodanine as functional group (RDSG) was prepared. Its adsorption and separation characteristics for Ag(I), Au(III) and Pd(II) were studied by flow-injection (FI) on-line preconcentration. Influence of different experimental parameters such as acidity, eluent, co-existing ions were investigated. Trace amounts of Ag, Au and Pd could be efficiently adsorbed by rhodanine-bonded silica gel from acidic solution and eluted with thiourea solution. Common co-existing ions exhibited virtually no interference to the preconcentration and determination. The adsorption capacity of RDSG was 0.0352, 0.107 and 0.122 mmol/g for Ag, Au and Pd, respectively. Detection limits of 0.004, 0.022 and 0.019 microg/mL for Ag, Au and Pd, respectively, were achieved with a sampling time of 60 s at a flow rate of 5.0 mL/min. The relative standard deviation were 0.5%, 0.9% and 1.7% for 0.040 microg/mL Ag, 0.200 microg/mL Au and 0.300 microg/mL Pd. The sorption property did not change after 1,000 cycles of sorption-desorption. The contents of Ag and Au in three national certified ore samples and Pd in a secondary nickel alloy, an anode slime and a CoCl2 electrolytic solution were determined. The results showed good agreement with the certified values.
 ...
PMID:Synthesis of rhodanine-bonded silica gel and its application in the preconcentration and separation of noble metals. 1122 14


1 2 3 4 5 6 7 8 9 10 Next >>