Showing papers on "Zinc published in 1983"

Structure and mechanism of copper, zinc superoxide dismutase

Abstract: Copper, zinc superoxide dismutase (SOD) catalyses the very rapid two-step dismutation of the toxic superoxide radical (O−2) to molecular oxygen and hydrogen peroxide through the alternate reduction and oxidation of the active-site copper1. We report here that after refitting and further refinement of the previous 2 A structure of SOD2, analysis of the new model and its calculated molecular surface shows an extensive surface topography of sequence-conserved residues stabilized by underlying tight packing and H-bonding. There is a single, highly complementary position for O−2 to bind to both the Cu(II) and activity-important Arg 141 with correct geometry; two water molecules form a ghost of the superoxide in this position. The geometry and molecular surface of the active site, together with biochemical data, suggest a specific model for the enzyme mechanism.

Effect of Soil pH on Adsorption of Lead, Copper, Zinc, and Nickel

Abstract: Lead, copper, nickel, and zinc adsorption by and desorption from pH-adjusted soils has been studied. Surface and subsurface horizon samples of two soils were equilibrated with varying amounts of Ca(OH)/sub 2/ prior to metal addition. The amount of all four metals retained was dependent upon pH of the soil sample, with retention dramatically increasing above pH 7.0 to 7.5. With the exception of Ni, at least 70 to 75% of the retained metal was extractable in 0.01N HCl. Nickel was somewhat less extractable, with that sorbed by the highest pH soils being the least extractable. Based on subsequent extractibility, the soils used appeared to have specific adsorption sites for Pb, Ni, and Cu but little or none for Zn. These studies cast some doubt on the concept of pH management for immobilizing heavy metals placed on the land in that sorbed metals were substantially extractable by 0.01M HCl, which has been used to estimate plant availability of soil ions.

Protein-free culture medium

Abstract: A trace element mixture suitable for use in a protein-free tissue culture medium, which comprises water-soluble compounds selected from acids, bases, and salts containing copper, iron, zinc, manganese, silicon, molybdenum, vanadium, nickel, tin, aluminum, silver, barium, bromine, cadmium, cobalt, chromium, fluorine, germanium, iodine, rubidium, zirconium, or selenium, the compounds being devoid of any additional metals other than those present as positive ions selected from groups IA and IIA of the periodic table of elements, wherein the compounds produce a solution containing specified minimum concentrations of the listed elements when dissolved in an amount of water sufficient to produce a concentration for one of the elements equal to the corresponding minimum concentration of the one element while maintaining each remaining element at a concentration equal to or greater than the minimum concentration for the remaining element is disclosed along with cell culture media containing these trace elements and methods of culturing cells using these media.

A reference method for measurement of alkaline phosphatase activity in human serum.

Abstract: We present an official AACC reference method for the measurement of alkaline phosphatase, the culmination of optimization experiments conducted by a group of independent laboratories. The details of this method and evaluation of factors affecting the measurement are described. A metal ion buffer has been incorporated that maintains optimal and constant concentrations of zinc(II) and magnesium(II) ions. Final reaction conditions are: pH (30 degrees C), 10.40 +/- 0.05; 2-amino-2-methyl-1-propanol buffer, 0.35 mol/L; 4-nitrophenyl phosphate, 16.0 mmol/L; magnesium acetate, 2.0 mmol/L; zinc sulfate, 1.0 mmol/L; and N-(2-hydroxyethyl)ethylenediaminetriacetic acid, 2.0 mmol/L.

Distribution and forms of copper, zinc, cadmium, iron, and manganese in soils near a copper smelter1

Abstract: We examined the contamination of soil by copper, zinc, and cadmium with respect to distance from a copper smelter. The majority of contamination was in the immediate vicinity of the smelter. Between 30 to 60 percent of total Cd was exchangeable in MgCl2 solution, and the exchangeability was much greater than that of the other elements examined, including iron and manganese. Most of the Cu, Zn, and Mn were present in an oxalate-extractable fraction, but only small amounts were extractable by citrate-dithionite-bicarbonate (CDB) solution. This suggests that Cu, Zn, and Mn were more strongly associated with amorphous iron oxides, with only small amounts being occluded in crystalline iron oxides. Only Cu was appreciably associated with the soil organic fraction. The treatment of soils with sodium hyperchlorite prior to oxalate extraction appeared to be necessary to better estimate the amounts of Cu associated with the oxalate-extractable fraction. Without this pretreatment, the oxalate extraction could overestimate the amounts of Cu associated with this particular fraction possibly due to the dispersion of organically complexed Cu in the oxalate solution. The mobility of Cu, Zn, and Cd in the soils was limited, as evidenced by a sharp reduction in concentrations of the three elements with depth. Comparing subsoil concentrations of these elements with those from areas relatively unpolluted by smelter fallout revealed that Cd was more leachable than Cu or Zn under western Washington conditions.

Intrinsic defects in ZnO varistors

Abstract: Theoretical calculations are presented for equilibrium concentrations of zinc and oxygen vacancies in ZnO. Results are presented at the sintering temperature, and also at room temperature. Theoretical calculations of reaction constants show that the intrinsic donor is the oxygen vacancy, rather than the zinc interstitial. The depletion of vacancies in the surface region, as the ZnO is cooled from the sintering temperature, is also calculated. Homojunction effects which are caused by such depletion are shown to be small.

Zinc and Infection

Abstract: Zinc is necessary for the normal functioning of all living systems. In microbes and mammals vital biological roles of zinc include the presence of this metal in metalloenzymes and membrane stabilization. In addition, zinc may bind nonspecifically to sulfhydryl, histidine, or other moieties on membranes, enzymes, or other proteins and alter their activity. Serum levels of zinc decrease sharply in many infections. Levels slightly below normal seem to be associated with optimal phagocytic function, and low concentrations of zinc may decrease microbial virulence. Brief decreases in serum levels appear to have no detrimental effect on host immunity and may act as a protective measure by decreasing the ability of indigenous or infecting microbes to thrive. However, prolonged zinc deficiency in mammals is associated with depressed T-cell function but near normal B-cell function. More work is needed for better understanding of zinc-related biochemistry and for determining the relationship between zinc status and susceptibility to infection in mammals.

Composition of the major elements and trace elements of 10 methanogenic bacteria determined by inductively coupled plasma emission spectrometry.

Abstract: The elemental composition of 10 methanogenic species was determined by inductively coupled plasma emission spectrometry and by a C-H-N-analyzer. The 10 species were representative of all three orders of the methanogens and were cultivated under defined conditions. Special emphasis was given toMethanosarcina barkeri, represented by 5 strains and cultivated on various substrates. The following elements with the lowest and highest values in parentheses were determined: C (37–44%, w/w), H (5.5–6.5%), N (9.5–12,8%); Na (0.3–4.0%), K (0.13–5.0%), S (0.56–1.2%), P (0.5–2.8%), Ca (order I: 85–550 ppm; order II: 1000–4500 ppm), Mg (0.09–0.53%), Fe (0.07–0.28%), Ni (65–180 ppm), Co (10–120 ppm). Mo (10–70 ppm), Zn (50–630 ppm), Cu (<10–160 ppm), Mn (<5–25 ppm). The biggest variations were found with respect to N and K, which both seem to have important physiological functions. Although it is unknown whether zinc and copper are essential trace elements for methanogens, all investigated species contained remarkably high zinc contents, whereas copper seemed to be present only in some species.

Surface characterization of copper(II) oxide-zinc oxide methanol-synthesis catalysts by x-ray photoelectron spectroscopy. 1. Precursor and calcined catalysts

Abstract: A surface characterization of the precursor and calcined copper oxide-zinc oxide (CuO-ZnO) catalysts prepared both by coprecipitation and by impregnation methods was carried out by using x-ray photoelectron spectroscopy (XPS). Strong oxide-oxide interactions were found to result in the formation of several surface copper species in the coprecipitated catalysts. With the catalysts containing 80-30 wt % CuO, it is proposed that the CuO structure is distorted to produce amorphous copper oxide phases in the surface layer. The copper species in the catalysts with > 80 wt % CuO are composed of the Cu/sup 2 +/ ions in crystalline CuO and the amorphous phases. As for the catalysts containing less than 30 wt % CuO XPS results showed the presence of Cu/sup 2 +/ ions, which dissolved substitutionally in the ZnO lattice and formed highly covalent bondings with oxygen anions. In contrast to the coprecipitated catalysts, the impregnated catalysts showed no appreciable interactions between copper and zinc oxides. The surface copper species in the precursor catalysts were attributed to copper hydroxycarbonate in the high copper content catalysts and to the copper in zinc hydroxycarbonate in the low copper content catalysts. 5 figures, 3 tables.

Surface characterization of copper(II) oxide-zinc oxide methanol-synthesis catalysts by x-ray photoelectron spectroscopy. 2. Reduced catalysts

Abstract: The surface state of the coprecipitated cupric oxide-zinc oxide (CuO-ZnO) catalysts reduced at 250/sup 0/C with H/sub 2/ was investigated by x-ray photoelectron spectroscopy (XPS). It was found that a monovalent copper species was present in the surface of the catalysts with low copper contents. It was revealed that two distinct types of copper metal species, both of them being negatively charged by electron transfer from ZnO, were produced in the catalyst surface upon the reduction. In the high copper content catalysts (> 25 wt % CuO), the predominant Cu metal species is described by well-dispersed metal particles, whereas in the low copper content catalysts (< 10 wt % CuO), the major copper metal species is best characterized by a two-dimensional epitaxial copper layer over ZnO. It is concluded that both the two-dimensional copper metal and Cu/sup +/ are formed from Cu/sup 2 +/ dissolved in a ZnO lattice, while the copper metal particles are originating mainly from crystalline and amorphous copper oxide phases. The two-dimensional copper metal species was found to be preferentially reoxidized to Cu/sup +/ when exposed to air at room temperature. The two-dimensional Cu/sup 0/-Cu/sup +/ species are suggested to be catalytically active for the methanolmore » synthesis at low temperature and pressure. The reduction of ZnO was observed only when reduced at 500/sup 0/C and in the presence of copper. In the case of the impregnated catalysts, no appreciable interactions were found between Cu metal and ZnO, in contrast to the coprecipitated catalysts. 7 figures, 2 tables.« less

The effect of pH on the total and free ionic concentrations of mnganese, zinc and cobalt in soil solutions

Abstract: Summary Samples of five soils whose pH in the field had been adjusted to between 5.0 and 7.5 were incubated with water or 0.01 m CaCl2 at 90% field capacity. Additional samples of the most acid soil were limed to various pH values immediately before incubation. Manganese, zinc and cobalt concentrations in the soil solutions, collected by displacement, decreased as the pH increased; the concentrations in calcium chloride solutions were higher than those in water solutions. The free divalent ions Mn2+, Zn2+ and Co2+ were the major metal species in solution at pH 5 but the proportion of the metals present as the free ion decreased as the pH increased. Differences in the manganese and zinc concentrations in the solutions were due not only to the pH of these solutions but also to the original pH of the soil in the field.

Dietary Zinc Requirement of Fingerling Channel Catfish

Abstract: Two experiments were conducted in order to establish the essentiality of zinc for fingerling channel catfish (Ictalurus punctatus) and to determine their dietary zinc requirement. Purified egg white diets with and without supplemental zinc were fed to channel catfish fingerlings for 12 weeks in the essentiality experiment. Catfish fed the basal diet containing 1.0 - 1.5 mg Zn/kg diet developed deficiency signs such as anorexia and suppressed growth. After week 8 of this experiment, two groups of fish fed the basal diet were converted to the zinc-supplemented diet, which contained 28 mg Zn/kg diet. Deficiency signs in these fish were alleviated after consumption of the zinc-supplemented diet. In the requirement experiment, graded levels of a zinc premix were added to egg white diets and fed to fingerling channel catfish for 14 weeks. Serum alkaline phosphatase, serum zinc, bone zinc and bone calcium data indicated that the minimum zinc requirement of fingerling channel catfish was 20 mg Zn/kg dry diet.

Zinc transport by brush border membrane vesicles from rat intestine.

Abstract: Zinc uptake into isolated brush border membrane vesicles from rat intestine was investigated by using a rapid filtration technique. Uptake was saturable at 0.2 mM extravesicular zinc, while at 1.0 mM zinc uptake was nonsaturable. ATP and Na+ did not stimulate uptake. Some binding of zinc was noted at zero intravesicular space indicating some membrane binding may occur during transport. Initial rates of uptake were linear up to 0.3 and 0.45 mM extravesicular zinc with vesicles prepared from rats fed adequate and deficient amounts of zinc, respectively. Kinetic analysis of uptake data yielded a Km of 0.38 mM and Jmax of 5.4 nmol X minute-1 X mg protein-1 with vesicles from zinc-adequate rats. With vesicles from zinc-depleted rats the Km was 0.44 mM and Jmax was 12.0 nmol X minute-1 X mg protein-1. These uptake data suggest the brush border membrane transport system for zinc is influenced by zinc status.

Iron superoxide dismutase from Escherichia coli at 3.1-A resolution: a structure unlike that of copper/zinc protein at both monomer and dimer levels.

Abstract: The structure of iron superoxide dismutase (EC 1.15.1.1) from Escherichia coli has been determined at 3.1-A resolution. The dimeric molecule is constructed from identical subunits, which are two-domain polypeptides. The NH2-terminal domain is composed of two antiparallel crossing helices and the COOH-terminal domain is a three-layered structure characterized by mixed alpha/beta secondary structural features. The active center iron atoms, separated by 18 A and located near the monomer-monomer interface, are coordinated by two amino acid residues from each domain. Azide binding has been investigated by using difference Fourier techniques. Consistent with the notion of the independent evolution of the copper/zinc dismutase gene, the iron dismutase structure resembles the copper/zinc protein at neither the monomer nor the dimer level.

Studies on the Bioavailability of Zinc in Humans: Mechanism of the Intestinal Interaction of Nonheme Iron and Zinc

Abstract: The mechanisms of the previously described competitive zinc:iron interaction were explored in healthy human volunteers, using the increment in plasma zinc concentration after an oral dose of 25 mg of zinc as zinc sulfate as the index of zinc absorption. Ferric iron in a 2:1 Fe/Zn ratio reduced the plasma uptake of zinc, but to a significantly lesser degree than ferrous iron; addition of 1 g of ascorbic acid increased the magnitude of the inhibitory effect of ferric iron to that seen with ferrous iron. An inverse relationship between some indices of iron status in adult women, or of parenteral iron administration in a child, and the magnitude of zinc:iron interaction was observed. Saturation of the intestinal mucosa with consecutive-day doses of therapeutic iron did not influence the uptake of zinc administered alone or in the context of a 2:1 ferrous iron:zinc ratio in solution. The results are most consistent with a combination of an intraluminal competition of the two minerals and an intracellular competition at a site "distal" to the regulatory step by which iron nutriture modulates the entry of iron into the body, but "proximal" to the site at which the daily administration of therapeutic doses of iron blocked the passage of dietary iron.

Thermodynamic binding constants of the zinc-human serum transferrin complex

Abstract: Serum transferrin is a mammalian iron-transport protein. It has two specific metal-binding sites that bind a variety of metal ions in addition to ferric ion. Equilibrium constants for the binding of zinc(II) have been determined by difference UV titrations using nitrilotriacetic acid and triethylenetetramine as competing ligands. The values are log K1* = 7.8 and log K2* = 6.4 in 0.10 M N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid and 15 mM bicarbonate, pH 7.4 at 25 degrees C. Titrations of the two forms of monoferric transferrin show that K1* corresponds to zinc binding to the C-terminal site and K2* corresponds to binding at the N-terminal site. These results indicate that at serum bicarbonate concentrations, transferrin should have a higher affinity for zinc(II) than serum albumin and therefore could play some role in zinc transport. A linear free-energy relationship has been constructed which relates the formation constants of a series of zinc(II) and iron(II) complexes. On the basis of the zinc-transferrin binding constants, this relationship has been used to estimate an iron(II)-transferrin binding constant of 10(7.4). Using this ferrous constant and literature values for the ferric transferrin binding constant, one calculates a ferric transferrin reduction potential of -140 mV, which is easily within the range of physiological reductants. Such a result tends to support mechanisms for iron removal from transferrin in which the ferric ion is reduced to the less tightly bound ferrous ion.

Copper and zinc species in the soil solution and the effects of soil pH

Abstract: A scheme to distinguish various species of trace metals in the soil solution has been used to study the forms of copper and zinc in the soil solution of a sandy loam that had been limed to give a range of soil pH values. The scheme is based on the lability of the metal species and involves the use of anodic stripping voltammetry, atomic absorption spectroscopy, and equilibration with Chelex-100 exchange resin. The solubility of zinc in this soil decreased markedly with increasing soil pH, with most of the zinc being present as free metal ions or as labile complexes. In contrast, copper species were largely moderately labile and non-labile and the solubility of copper varied only slightly with soil pH. The effects of enriching the soil with the metals and organic matter on the species present were also investigated.

Severe Zinc Deficiency: Effects on the Distribution of Nine Elements (Potassium, Phosphorus, Sodium, Magnesium, Calcium, Iron, Zinc, Copper and Manganese) in Regions of the Rat Brain

Abstract: The effect of severe zinc deficiency on the distribution of nine elements (potassium, phosphorus, sodium, magnesium, calcium, iron, zinc, copper and manganese) in brain regions (olfactory lobes, right and left hippocampi, cerebellum and the rest of the brain) has been studied. After male rats (30 days old) were fed a zinc-deficient diet for 28 days, the zinc concentration of most brain parts was similar to zinc-adequate control values. Olfactory lobe zinc, on the other hand, was slightly depressed. However, the levels of other metals were dependent on zinc nutriture. Zinc deficiency caused an elevation in copper concentrations in most brain parts. Restriction of food intake caused a similar increase in brain copper but generally the effect was less than with zinc deficiency. Levels of calcium, manganese, sodium and potassium, in certain brain regions, also appeared to be altered by the zinc status of an animal. Of the minerals examined, only zinc and copper displayed asymmetrical distribution between the right and left hippocampus, and severe zinc deficiency did not affect lateral distribution of these trace metals in the hippocampus. The data suggest the hypothesis that changes in brain metal content, associated with zinc deficiency, contribute to the behavioral abnormalities that occur.