Depletion Of Mg Research Articles

Interstitial water chemistry of the inner continental shelf sediments off the gironde estuary

The interstitial water composition ( SO 4 2− , alkalinity, Ca 2+, Mg 2+, Sr 2+, Na +, K +) and the cation exchange capacity (CEC) were determined for the muddy sediments of the continental shelf off the Gironde Estuary (France), in the area where the sediment represents the deposit of the muddy suspension of the river. In comparison with seawater concentrations, the pore waters below 10 cm depth, show depletions of SO 4 2− and Ca 2+ and below a 30 cm depth show depletions of Mg 2+. Inversely, the upper 10 cm an enrichment of Ca 2+ concentration, and an increase of K + concentration to a 40 cm depth. High values of SO 4 2− are observed at the top 4 cm. Alkalinity enrichment is observed along the length of the core. Applying the alkalinity models for the sediment below a 10 cm depth demonstrates generally that calculated alkalinities are higher than the measured ones. Ca 2+ dissolution occurs at the first 10 cm and authigenic carbonate precipitation starts beneath that level. Mg 2+ depletion is accompanied by bicarbonate loss. This proves that Mg 2+ depletion is due to a Mg-silicate reaction. The result of the CEC does not confirm the Mg 2+ uptake by clay minerals in exchangeable site, under reducing conditions. Diffusion and bioturbation play an important role in the pore water concentration at the top of the core.

Toxicological and pharmacological studies on magnesium deficiency in rats: Histamine-metabolizing enzymes in some tissues of magnesium-deficient rats.

The effects of dietary magnesium(Mg) deficiency on histamine-metabolizing enzymes were studied in young Wistar rats with a mean initial body weight of 60 g. Histidine decarboxylase(HDC) activity was observed in the stomach, skin, lung, spleen and liver, but not detected in the duodenum or kidney in the control rats. In 4 days of feeding an Mg-deficient diet(Mg:0.001%), the HDC activity of the spleen, lung and liver appeared to rise until the 8th day of Mg deficiency. In the skin, the HDC activity was the highest on the 4th day of Mg deficiency, then decreased on the 6th day, and increased again on the 8th day. Diamine oxidase(DAO) activity was high in the duodenum, but low in the other tissues examined in control rats. In 2 to 4 days of depletion of Mg in the diet, the DAO activity decreased in all the tissues examined to about 1/2 that of the control group. Histamine methyl transferase(HMT) activity was high in the kidney, liver and duodenum in control rats. HMT activity observed in these tissues did not change significantly during the 8-day Mg absence in the diet. These results suggest that both the increased HDC and the decreased DAO activities contribute to the increase in the histamine content in some tissues in Mg-deficient rats.

Isolation and characterization of terminally differentiated chicken and rat skeletal muscle myoblasts

The ability of skeletal muscle myoblasts to differentiate in the absence of spontaneous fusion was studied in cultures derived from chicken embryo leg muscle, rat myoblast lines L6 and L8, and the mouse myoblast line G8. Following 48–96 hr of culture in a low-Ca 2+ (25 μm), Mg 2+-depleted medium, chicken myoblasts exhibited only 3–5% fusion whereas up to 64% of the cells fused in control cultures. Depletion of Mg 2+ led to preferential elimination of fibroblasts, with the result that 97% of the mononucleated cells remaining at 120 hr exhibited a bipolar morphology and stained with antibodies directed against M-creatine kinase, skeletal muscle myosin, and desmin. Mononucleated myoblasts rarely showed visible cross-striations or M-line staining with anti-myomesin unless the medium was supplemented with 0.81 m M Mg 2+, suggesting that Mg 2+ plays a role in sarcomere assembly. Conditions of Ca 2+ and Mg 2+ depletion inhibited myoblast fusion in the rodent cell lines as well, but mononucleated myoblasts failed to differentiate under these conditions. Differentiated individual myoblasts from rat cell lines and from chicken cell cultures were obtained when fusion was inhibited by growth in cytochalasin B (CB). CB-treated rat myoblast cultures accumulated MM-CK to nearly twice the specific activity found in extensively fused control cultures of comparable age. Spherical cells which accumulated during CB treatment were isolated and shown to contain nearly eight times the CK specific activity present in nonspherical cells from the same cultures. Approximately 90% of these cells exhibited immunofluorescent staining with antibodies to skeletal muscle myosin, failed to incorporate [ 3H]thymidine or to form colonies in clonal subculture, and thus represent terminally differentiated rat myoblasts. Quantitative microfluorometric DNA measurements on individual nuclei demonstrated that the terminally differentiated myoblasts obtained in these experiments from both chicken and rat contain 2cDNA levels, suggesting arrest in the G 0 stage of the cell cycle.

The effect of redox potential on the kinetics of fluorescence induction in pea chloroplasts. II. Sigmoidicity

The shape of the fluorescence induction curve in chloroplasts inhibited by 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea has been determined at different redox potentials. At −10 mV a monophasic and sigmoidal curve is seen which is transformed into an exponential curve when the potential is poised at −150 mV. At this potential, the quencher with high midpoint, Q H, is reduced but that with low midpoint, Q L, is oxidized. Thus, a sigmoidal induction is observed during photoreduction of Q L and Q H but photoreduction of Q L proceeds with exponential kinetics. A correlation between the relative proportions of Q L and Q H observed in redox titration and the sigmoidicity of induction is also seen upon depletion of Mg 2+ and after alkalinization to pH 9.5. Several models are discussed to explain the relationship between Photosystem II interactions and Q heterogeneity.

The composition and diagenesis of interstitial solutions—II. Fluxes and diagenesis at the water-sediment interface in the high latitude North and South Atlantic

Studies of the major element composition of in situ sampled pore waters are reported for the North Atlantic and Southern Ocean between Africa and Antarctica. The pattern of diagenetic modification of pore water composition is similar throughout the entire Atlantic. Enrichment of Na +, Ca 2+ and alkalinity and depletion of Mg 2+ and K + are nearly universal. Only siliceous oozes consistently provide very limited evidence of cation diagenesis. The changes observed and the calculated fluxes across the seawater-sediment interface are much the same as those reported previously for other areas of the Atlantic and Caribbean. Fluxes of the major cations across the interface continue to be indicated as a major factor in the geochemical cycling of these elements, particularly Na +, Mg 2+ and K +. Diagenetic modelling indicates that aerobic oxidation of organic matter and consequent dissolution of CaCO 3 is a dominant reaction throughout the North Atlantic. The data indicate that O 2 oxidation to at least 30 cm is prevalent at nearly all stations. Dissolution of CaCO 3 in response to the introduction of metabolic CO 2 can lead to significant post-depositional modification of the sediments. The modelling also indicates a 1:1 stoichiometric relationship between Na + release and Mg 2+ uptake by sedimentary components. Although dissolved silica concentrations in biogenic siliceous sediments are among the highest yet reported (>700μM), calculations demonstrate that solubility control cannot be through equilibria with the mineral sepiolite. Further, the influence of cation-silicate surface phases, generally, upon solubility is contraindicated by Si(OH) 4-Mg 2+-H + relationships. Evaluation of the influence of fluid advection on pore water profiles indicates that at the stations studied in the North Atlantic, it is small. A more general consideration of the potential contribution of fluid advection to shaping interstitial water profiles demonstrates that advection can be a dominant factor. In such circumstances, serious misinterpretation of the nature of diagenetic reactions may result from a lack of knowledge and consideration of fluid advection.

Evidence for MG and /Fe, Si/ phase separation in interstellar dust

view Abstract Citations (13) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Evidence for Mg and /Fe, Si/ phase separation in interstellar dust Duley, W. W. Abstract Analysis of the depletions of Mg, Si, and Fe in diffuse clouds shows that distinct Mg-rich and (Fe, Si)-rich dust components exist in diffuse clouds. It is unlikely that more than 65% of interstellar Mg is ever contained in silicates. Depletion in diffuse clouds may occur by selective accretion on (Fe, Si)-oxide cores. Publication: The Astrophysical Journal Pub Date: August 1980 DOI: 10.1086/183321 Bibcode: 1980ApJ...240L..47D Keywords: Astrophysics; Interstellar Matter; Iron Compounds; Magnesium; Phase Separation (Materials); Silicon Compounds; Abundance; Cosmic Dust; Infrared Spectra; Astrophysics full text sources ADS |

Transport of mono- and divalent cations across chloroplast membranes mediated by the ionophore A23187

Effects of the ionophore A23187 on isolated broken and intact chloroplasts in the pH range of 6.2 to 7.6 have been studied. In both types of chloroplasts, uncoupling of photosynthetic electron transport by A23187 (6–10 μ m) was mediated either by Mg 2+ or—in the absence of divalent cations (i.e., when EDTA was added to the medium)—by high concentrations of Na +, but not of K + ions. At increased concentrations of the ionophore (above about 10 μ m) and high pH (7.2 to 7.6), uncoupling in broken chloroplasts was also mediated by K + ions. The inhibition of the energy-dependent slow decline of chlorophyll fluorescence in intact chloroplasts by the ionophore (which denotes uncoupling) is reversed by EDTA in the presence of K +, but not of Na + ions. In 3-(3′,4′-dichlorophenyl)1,1-dimethylurea-poisoned intact chloroplasts, the yield of variable chlorophyll fluorescence is lowered by A23187 + EDTA and increased again by addition of NaCl or KCl. Chlorophyll fluorescence spectra at 77 °K of intact chloroplasts incubated with A23187 + EDTA indicated that the distribution of excitation energy had changed in favor of photosystem I, as expected from a depletion of Mg 2+. This change was reversed by MgCl 2+, KCl, or NaCl. From a comparison of low-temperature fluorescence spectra of broken and intact chloroplasts at different levels of Mg 2+ in the medium, the concentration of free Mg 2+ in the stroma of the intact chloroplasts at pH 7.6 in the dark was estimated at 1 to 4 m m. The results show that in chloroplasts the specificity of A23187 for divalent cations is limited. In the presence of EDTA, the ionophore mediates fast Na + H + exchange across thylakoid membranes, whereas K + is transferred much less efficiently. Both Na + and K + ions seem to be transported readily across the chloroplast envelope by the action of the ionophore, leading to an exchange of Mg 2+ for monovalent cations at the thylakoid membrane surfaces in intact chloroplasts.

Orca Basin: Depositional processes, geotechnical properties and clay mineralogy of Holocene sediments within an anoxic hypersaline basin, northwest Gulf of Mexico

The central part of Orca Basin, an intraslope basin in the northwest Gulf of Mexico, is anoxic and hypersaline. High-resolution seismic profiles show deformed parallel reflectors along the periphery of the basin, diffractions and indications of slump scars on the slopes, and chaotic reflectors on the basin floor. Calculated sedimentation rates in excess of 1 m 1000 years and reflector configurations indicate that mass movement is the primary mechanism for sediment accumulation within the basin. Variations in the sediment properties and constituents indicate that slumping has occurred from within and from outside the brine portion of the basin. Sediment water contents exceeding 100% to depths in excess of 10 m are a result of rapid sediment accumulation, a high percentage of smectite, and a highly compressible sediment microstructure having open arrangement. These conditions suggest original deposition within the brine and subsequent slumping into the deepest part of the basin. Clay mineral variations within the brine are directly related to: (1) pore water enrichments of Na + and Ca 2+ and a depletion of Mg 2+ with respect to normal seawater; (2) the underconsolidated nature of the sediments; (3) the time in which the clay minerals are in contact with these conditions; and (4) if deposited by mass movement, the original site of deposition with respect to the location of the brine. Sediments originally deposited outside and subsequently transported into the brine part of the basin by mass movement have properties and clay mineral abundances characteristic of normal continental slope sediments.

Adsorption properties of U.I.C.C. Rhodesian chrysotile and crocidolite in aqueous solution -- effects of cation depletion.

Adsorption properties of U.I.C.C. Rhodesian chrysotile and crocidolite were tested in aqueous solution with acid and basic dyes (Eosine Y. Picric Acid, Acridine Orange and Methylene Blue). Rates of adsorption showed a diffusion of only basic dyes in micropores of fibers. The strong adsorption of basic dyes on the surface of the fibers led us to suppose that the active sites have a negative charge. Our hypothesis was supported by the verification of an increase in adsorption capacity whick depends on depletion of Mg++ from chrysotile and of Fe+++ from crocidolite.

Removal of magnesium from interstitial waters in reducing environments—the problem reconsidered

Iron-containing smectites are not affected significantly by Mg-containing dilute sulphide solutions. Concentrated solutions reduce most of the Fe in montmorillonites; Fe is partially extracted from nontronite with concomitant disintegration of the structure. It is concluded that direct Mg → Fe exchange in clays seems improbable, but that depletion of Mg in interstitial waters of anoxic sediments may be due to reaction of Mg-containing solutions with partially disintegrated clay.

Mg 2+-ATPase as a membrane ecto-enzyme of human granulocytes. Inhibitors, activators and response to phagocytosis

1. (1) The Mg 2+-ATPase of purified human granulocytes is located at the plasma membrane. Thus, no additional enzyme activity was detected when the cells were disrupted. Moreover, the Mg 2+-ATPase activity of intact cells was inhibited by such poorly permeant reagents as diazotized sulfanilic acid and suramin. Finally, the enzyme activity of cell homogenates was recovered in particulate fractions. 2. (2) The surface Mg 2+-ATPase of human granulocytes had an apparent K m of 50 μM for ATP and displayed substrate inhibition. 3. (3) The enzyme was not affected by ouabain, but was inhibited by N- ethyl maleimide , sodium meta-periodate, suramin and diazotized sulfanilic acid. The enzyme was activated by cytochalasins B and D and by UDP. Activation by UDP was characterized by changes in the enzyme's apparent K m and V and by relief of substrate inhibition. 4. (4) Internalization of surface membranes subsequent to phagocytosis of suitable particles did not result in depletion of Mg 2+-ATPase from the cell surface. The enzyme activity did not decrease after exposure to several varieties of paraffin oil emulsion particles, even if the challenged cells had been pretreated with colchicine or cytochalasin B. 5. (5) Since suramin, which inhibited Mg 2+-ATPase, had no effect upon other granulocyte functions such as chemotaxis, superoxide anion generation, or phagocytosis, it is unlikely that the enzyme plays a major role in these functions.

Influence du fluor sur la composition minerale d'aiguilles polluees de sapin ( Abies alba Mill.)

Chemical composition of fir needles is modified by elevated fluorine accumulation. Our results indicate that fluoride pollution tends to reduce the concentration of Mg and Mn and to increase that of Ca and F. They also indicate that fluorine level has no consistent effect on levels of major nutrient elements, e.g. N, P and K. Nevertheless, from an internal fluorine accumulation of 400 ppm, depletion of Mg and Mn and higher fluorine level had no significant effect on levels of the remaining elements. Moreover, a very similar depletion of Mg and Mn with fluorine accumulation is observed and a positive correlation may be found between these two elements.

Clinopyroxenes and Coexisting Mafic Minerals from the Alkaline Ilimaussaq Intrusion, South Greenland

The Ilímaussaq intrusion consists of an augite syenite shell and a central cumulitic series of layered peralkaline (agpaitic) nepheline syenites with both roof and bottom cumulates. Microprobe analyses of the strongly zoned mafics show that the pyroxenes range from ferro-salite through hedenbergite to aegirine, the amphiboles from hastingsite through katophorite to arfvedsonite, and the olivines from Fo16.8 to FO0.2. Aenigmatite analyses are also presented. The crystal chemistry of the pyroxenes is discussed in detail. The behaviour of the various elements is discussed in relation to the conditions in the coexisting magma. The relation between oxygen fugacity and silica activity and the stability of fayalite and Na-poor pyroxenes in over-and undersaturated magmas is considered. The persistent stability of these minerals in the strongly undersaturated Ilimaussaq magma shows that the oxygen fugacities in Ilímaussaq were lower than in any other known alkaline suites. Based on the compositional development in the mafic minerals it is inferred that the intrusion formed from at least three separate pulses of successively more differentiated magma: (1) an augite syenite magma congealed inwards from the sides, (2) a peralkaline undersaturated magma gave rise to the roof cumulates which congealed successively downwards. The differentiating magma was water-undersaturated and underwent depletion in Mg and enrichment in Zr and Na. The contemporaneous bottom cumulates are hidden beneath the now visible bottom cumulates which possess a still more differentiated liquidus mineral assemblage and are ascribed to a third separate magma pulse.

Mg, Ca and [formula omitted] exchange in the sediment-pore water system, hole 149, DSDP

The diagenesis and geochemical evolution of deep-sea sediments are controlled by the interaction between sediments and their associated pore waters. With increasing depth, the pore water of Hole 149 (DSDP) exhibits a strong depletion in Mg and a corresponding enrichment in Ca, while the alkalinity remains relatively constant. Dissolved SiO 2 is nearly constant in the upper 100 m of sediment, but is highly enriched in the deepest pore waters. The pore waters exhibit a depletion in K with increasing depth, and O 18 O 16 pore water ratios also decrease. The sediment section has three zones of sedimentary regimes with increasing depth in the drill hole: an upper 100 m section of detrital clays, a middle section enriched in calc-akalic volcanics which have undergone submarine weathering to a smectite phase, and a lower section of siliceous ooze which still has a diagenetic smectite phase. The quartz-feldspar ratios and O 18 O 16 composition of the silicate phases are in agreement with these interpretations. The submarine weathering of volcanics to a smectite can account for the observed pore water gradients. Volcanics release Ca and Mg to the pore waters causing the alkalinity values to increase. Smectite is formed, depletes the pore waters in Mg and O 18 and causes the alkalinity to decrease. The net reaction allows for the observed relationship between pore water Ca and Mg gradients with little net change in alkalinity. Given the abundance of volcanics in many deep-sea sediments, especially in lower sections which often form near ridge crests, the submarine formation of smectite may be an additional oceanic Mg sink which has not yet been fully considered.

A geochemical study of silali volcano, Kenya, with special reference to the origin of the intermediate-acid eruptives of the central rift valley

The Rift Valley zone in East Africa may be regarded as an aborted ocean of long existence but never significantly opened up. Distensive regimes of tectonic up-doming, eruptivity and subsidence on normal faults, and median positive gravity anomalies complicating the wide negative gravity anomaly of Bullard must now be fitted into any model for the Rift Valley. The petrological and geochemical nature of the eruptives is equally important: it is common to equate the abundance of salic volcanics in any section with thickness of the sialic crust there, assuming sialic remelting or sialic contamination. The results of a detailed geochemical study of a single Quaternary caldera volcano, Silali, and its Plio-Pleistocene volcanic foundation are summarised here, and used as a model for differentiation in the central Gregory Rift Valley. A monistic differentiation theory must be sought to explain the peralkaline sialic eruptives, associated with alkalic basalts in great volumes, from the Miocene onwards. Relative to the basalts there is an increase in Si, Na, K and depletion of Mg, Ca, Ti; total iron shows slight depletion and the iron shows oxidation to the ferric oxide. Of the minor elements, Rb, Zn, Y, La, Zr, Pb, and Nb are increased; Cu, Ba and Sr depleted; and Cr, Co and Ni show slight depletion. The trends seen in trachytes, etc., are incipiently evident in hawaiites and mugearites. The consistent bimodality, peralkaline character of the intermediate to acid rocks, major and minor element contents, and intimate intermingling of the two suites in space and time, can only be interpreted in terms of complex differentiation process affecting a mantle-derived basalt parent. Comparisons are drawn with the volcanic suites of Tenerife and with a differentiated intrusion in Australia which shows bimodality as a product of differentiation. It is suggested that a chain of cupolas underlie the Rift Valley, and in these differentiation follows an agpaitic regime, under the control of volatile concentration. Such cupola reservoirs probably reach up close to the floor of the Rift Valley. The change from phonolite dominance to trachyte-comendite dominance in the intermediate suites is the only significant time progressive change evident from Miocene to Recent. Notwithstanding this, the intermediate-acid rocks, and basic rocks associated with them plot consistently on FMA and alkali silica diagrams throughout this period.