Elevated Zinc Research Articles

A Histidine-rich Cluster Mediates the Ubiquitination and Degradation of the Human Zinc Transporter, hZIP4, and Protects against Zinc Cytotoxicity

Zinc is an essential nutrient. Genetic evidence for this nutritional requirement in humans is the zinc deficiency disease, acrodermatitis enteropathica. This disorder is caused by mutations in hZIP4 (SLC39A4), a zinc importer required for zinc uptake in enterocytes and other cell types. Studies in mice have demonstrated that levels of the mZIP4 mRNA are reduced by elevated dietary zinc, resulting in a decreased abundance of the ZIP4 protein at the plasma membrane. Moreover, studies in cultured cells have demonstrated that low micromolar concentrations of zinc stimulate the endocytosis of the mZIP4 protein resulting in a reduction in cellular zinc uptake. In this study, we demonstrate an additional level of hZIP4 regulation involving ubiquitination and degradation of this transporter in elevated zinc concentrations. Mutational analysis identified a cytoplasmic histidine-rich domain that was essential for ubiquitin-dependent degradation of ZIP4 and protection against zinc toxicity. However, this motif was dispensable for zinc-induced endocytosis. These findings indicate that ubiquitin-mediated degradation of the ZIP4 protein is critical for regulating zinc homeostasis in response to the upper tier of physiological zinc concentrations, via a process that is distinct from zinc-stimulated endocytosis.

Transfer and loss of naturally-occurring plasmids among isolates of Rhizobium leguminosarum bv. viciae in heavy metal contaminated soils

Plasmid transfer among isolates of Rhizobium leguminosarum bv. viciae in heavy metal contaminated soils from a long-term experiment in Braunschweig, Germany, was investigated under laboratory conditions. Three replicate samples each of four sterilized soils with total Zn contents of 54, 104, 208 and 340 mg kg −1 were inoculated with an equal number (1×10 5 cells g −1 soil) of seven different, well-characterized isolates of R. leguminosarum bv. viciae. Four of the isolates were from an uncontaminated control plot (total Zn 54 mg kg −1) and three were from a metal-contaminated plot (total Zn 340 mg kg −1). After 1 year the population size was between 10 6 and 10 7 g −1 soil, and remained at this level in all but the most contaminated soil. In the soil from the most contaminated plot no initial increase in rhizobial numbers was seen, and the population declined after 1 year to <30 cells g −1 soil after 4 years. One isolate originally from uncontaminated soil that had five large plasmids (no. 2-8-27) was the most abundant type re-isolated from all of the soils. Isolates originally from the metal-contaminated soils were only recovered in the most contaminated soil. After 1 year, four isolates with plasmid profiles distinct from those inoculated into the soils were recovered. One isolate in the control soil appeared to have lost a plasmid. Three isolates from heavy metal contaminated soils (one isolate from the soil with total Zn 208 mg kg −1 and two isolates from the soil with total Zn 340 mg kg −1) had all acquired one plasmid. Plasmid transfer was confirmed using the distinct ITS–RFLP types of the isolates and DNA hybridization using probes specific to the transferred plasmid. The transconjugant of 2-8-27 which had gained a plasmid was found in one replicate after 2 years of the most contaminated soil but comprised more than 50% of the isolates. A similar type appeared in a separate replicate of the most contaminated soil after 3 years and persisted in both of these soils until the final sampling after 4 years. After 2 years isolates were recovered from four of the soil replicates with the chromosomal type of 2-8-27 which appeared to have lost one plasmid, but these were not recovered subsequently. Isolate 2-8-27 was among the isolates most sensitive to Zn in laboratory assays, whereas isolate 7-13-1 showed greater zinc tolerance. Acquisition of the plasmid conferred enhanced Zn tolerance to the recipients, but transconjugant isolates were not as metal tolerant as 7-13-1, the putative donor. Laboratory matings between 2-8-27 and 7-13-1 in the presence of Zn resulted in the conjugal transfer of the same small plasmid from 7-13-1 to isolate 2-8-27 and the transconjugant had enhanced metal tolerance. Our results show that transfer of naturally-occurring plasmids among rhizobial strains is stimulated by increased metal concentrations in soil. We further demonstrate that the transfer of naturally-occurring plasmids is important in conferring enhanced tolerance to elevated zinc concentrations in rhizobia.

Elevated zinc protoporphyrin/heme ratios in umbilical cord blood after diabetic pregnancy

Offspring of diabetes patients may suffer from tissue iron deficiency. Erythrocyte zinc protoporphyrin/heme (ZnPP/H) ratios measure impaired iron status. The aim of the study was to examine whether cord ZnPP/H ratios were associated with pregnancy glycemic control. ZnPP/H was measured in cord blood from 31 pregnancies with insulin-treated diabetes (diabetes group) and compared to population normal values. Maternal glycemic control was assessed by daily glucose log, glycosylated hemoglobin and birth weight. Median cord ZnPP/H was higher in the diabetes group than the population normal values (106 (65.2 to 146.8) microM/M vs 68.2 (37.6 to 98.8) micro/M, P < 0.0001). Ratios were directly correlated to surrogates of control (glycosylated hemoglobin, P = 0.05, and birth weight, P < 0.04). Cord ZnPP/H ratios from pregnancies with pre-existing and gestational diabetes were similar. Because cord ZnPP/H was higher in large offspring of diabetic pregnancy, it might identify greater iron utilization for fetal erythropoiesis.

PKR1 Encodes an Assembly Factor for the Yeast V-Type ATPase

PKR1 Encodes an Assembly Factor for the Yeast V-Type ATPase

Profound Copper Deficiency in a Patient with History of Gastric Bypass

Copper deficiency (hypocupremia) is a rare entity that can lead to serious morbidity. With advent of gastric bypass surgery, hypocupremia is being increasingly recognized in adult populations. We present a case patient with hypocupremia and profound neurological symptoms to stress the importance of this entity and its early diagnosis and treatment. We present a case of a 62 year-old white female who had Roux-en-Y gastric bypass surgery. Due to multiple nutritional deficiencies following surgery, she was receiving multivitamin supplements including iron and zinc supplementation as well as vitamin B12 injections. Ten years after her gastric bypass, she began having progressively worsening ataxia, paresthesias of lower extremities and hands, and generalized weakness. Her weakness continued to progress resulting in significant proximal muscle weakness as demonstrated by her difficulty in rising from seated position. Patient eventually became hospitalized for severe weakness requiring mechanical ventilation. On admission, an extensive nutritional evaluation was significant for undetectable copper level and elevated zinc level. MRI of spine showed abnormal T2 hyperintensity within the posterior columns of the spinal cord from the C7-T1 level to the skull base which has been previously described in patients with hypocupremia. Intravenous copper infusions were given to the patient during her hospitalization. She had dramatic clinical improvement which correlated with the normalization of serum copper level. The patient was eventually weaned from the ventilator and began demonstrating further improvement in her muscle weakness. Direct percutaneous endoscopic jejunostomy tube was placed and patient fed enterally. The patient was ambulatory prior to her discharge from the hospital. Hypocupremia is a rare complication following gastric bypass operation. Copper is primarlily absorbed in the stomach and proximal small bowel, however, it is uncertain why hypocupremia occurs only in certain patients following gastric bypass. Previous literature has established an association with zinc overload state and hypocupremia. Zinc and iron supplementation have already been demonstrated in animal models to inhibit copper uptake in the proximal gut. The combination of gastric bypass and zinc overload likely caused our patient's hypocupremia. Her dramatic improvement after aggressive copper replacement stresses the importance of the timely diagnosis and treatment of hypocupremia.

Long‐term exposure to elevated zinc concentrations induced structural changes and zinc tolerance of the nitrifying community in soil

A series of long-term Zn-contaminated soils was sampled around a galvanized pylon. The potential nitrification rate (PNR) was unaffected by the soil total Zn concentrations up to 25 mmol Zn kg(-1) whereas spiking the uncontaminated control soil with ZnCl(2) to identical total concentrations completely eliminated nitrification. The larger sensitivity of the PNR to spiked ZnCl(2) than to the Zn added in the field was equally found when relating the PNR to the Zn concentrations in the pore water of these soils, suggesting differences in Zn tolerance of the nitrifying communities. Zinc tolerance in the long-term Zn-contaminated soil was demonstrated by showing that (i) the nitrifying community of long-term Zn-contaminated soil samples was less sensitive to Zn than that of the uncontaminated control soil when both communities were inoculated in sterile ZnCl(2)-contaminated soil samples, and, that (ii) addition of ZnCl(2) to the long-term Zn-contaminated soil samples affected nitrification less than equal additions of ZnCl(2) to uncontaminated control samples. Denaturing gradient gel electrophoresis fingerprinting of polymerase chain reaction amplified 16SrRNA gene fragments of ammonia-oxidizing bacteria showed that the community structure in uncontaminated and long-term contaminated soil samples was different and could be related to soil Zn concentrations.

Elevated cortical zinc in Alzheimer disease

To determine whether changes in brain biometals in Alzheimer disease (AD) and in normal brain tissue are tandemly associated with amyloid beta-peptide (Abeta) burden and dementia severity. The authors measured zinc, copper, iron, manganese, and aluminum and Abeta levels in postmortem neocortical tissue from patients with AD (n = 10), normal age-matched control subjects (n = 14), patients with schizophrenia (n = 26), and patients with schizophrenia with amyloid (n = 8). Severity of cognitive impairment was assessed with the Clinical Dementia Rating Scale (CDR). There was a significant, more than twofold, increase of tissue zinc in the AD-affected cortex compared with the other groups. Zinc levels increased with tissue amyloid levels. Zinc levels were significantly elevated in the most severely demented cases (CDR 4 to 5) and in cases that had an amyloid burden greater than 8 plaques/mm(2). Levels of other metals did not differ between groups. Brain zinc accumulation is a prominent feature of advanced Alzheimer disease (AD) and is biochemically linked to brain amyloid beta-peptide accumulation and dementia severity in AD.

Comparative Effectiveness of Zinc Protoporphyrin and Hemoglobin Concentrations in Identifying Iron Deficiency in a Group of Low-Income, Preschool-Aged Children: Practical Implications of Recent Illness

The goal was to assess the influence of recent infection on screening tests for iron depletion (zinc protoporphyrin and hemoglobin) among low-income, preschool-aged children. This cross-sectional study was conducted at community sites and ambulatory care clinics in Hartford, Connecticut, and included 180 preschool-aged children. Iron depletion was defined as serum ferritin levels of < or = 15 microg/L. Recent illness was defined by parent or guardian (caretaker) report or evidence of elevated C-reactive protein concentrations. History of anemia was determined through medical records review. Sensitivity, specificity and positive predictive values of hemoglobin and zinc protoporphyrin were calculated overall and for children with and without recent illness. At enrollment, more than one half of the children had a recent illness, and 57.5% had a history of anemia. More than one third had iron depletion. Serum ferritin levels were significantly higher among recently ill children. Secondary to recent illness, the positive predictive value of elevated zinc protoporphyrin, but not low hemoglobin, was reduced significantly. Zinc protoporphyrin levels of >69 micromol/mol heme identified significantly more iron-deficient children. Compared with anemia, elevated zinc protoporphyrin levels identified significantly more iron-deficient children. Recently ill children were one half as likely to have low serum ferritin levels, compared with children without recent illness. The negative effect of recent illness on the positive predictive value of zinc protoporphyrin when ferritin is used to determine iron status has many practical implications.

Iron in the Brain

After completing this article, readers should be able to: 1. Describe the role of iron in proteins involved in neuronal and glial energy metabolism, myelin production, and monoamine neurotransmitter metabolism. 2. Indicate the neonates who are at risk for iron deficiency. 3. Explain how iron deficiency affects the biochemistry, structure, signaling molecules, and electrophysiology of the hippocampus. 4. Describe the primary causes of iron overload in the neonate. 5. Explain why the preterm infant is at particular risk for iron deficiency. This article is designed to acquaint readers with the role of iron in early brain development. Several important principles that govern the effects of nutrients on the immature brain are discussed, followed by an explanation of the roles of iron during development. Because the developing brain is sensitive to iron overload as well as iron deficiency, both are discussed in the context of human studies and in model systems. The first guiding principle of nutrient-brain interactions during development is the concept of timing, dose, and duration. (1) The positive or negative effects of any nutrient depend on which brain regions or processes are developing at the time that nutrient status is altered and the requirements of those regions for the nutrient during that time of development. Generally, the more rapidly an area is developing, the more vulnerable it is. Dependence on specific nutrients during phases of rapid proliferation or differentiation results in the second principle, a regionalization of brain effects during periods of nutrient deficiency. In the case of iron deficiency, certain brain areas that are dependent on iron for proper development are more vulnerable than areas that are less dependent on iron. Additionally, these same brain areas are likely to be more vulnerable at certain time points than at others. To exert a maximal effect on regional brain development, the timing of iron …

English

Mining wastes comprised of heavy metals and arsenic and deposited along Silver Bow Creek downstream of Butte, Montana have posed a threat to human health and the environment for over 100 years. Under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), the State of Montana has undertaken the remediation of more than three million cubic meters of mine waste deposited along approximately 40 kilometers of Silver Bow Creek and its floodplain. During remediation, mine waste is excavated from the stream and floodplain and the waste is placed in a regional repository or a local repository constructed for the project. The stream and floodplain have been rebuilt to restore their natural functions and maintain streambank stability during vegetation reestablishment. This paper presents results of water quality monitoring on Silver Bow Creek. Surface water and groundwater quality have greatly improved in the remediated reaches compared to pre-remediation conditions although copper and zinc still frequently exceed aquatic life standards. Some water quality problems persist including the elevated nutrient levels originating at the Butte wastewater treatment works and the elevated copper and zinc concentrations in groundwater, which affect aquatic life in surface water systems.

Anthropometric, environmental, and dietary predictors of elevated blood cadmium levels in Ukrainian children: Ukraine ELSPAC group

No comprehensive data on sources or risk factors of cadmium exposure in Ukrainian children are available. In this we measured the blood levels of cadmium among 80 Ukrainian children and evaluated sources of exposure. A nested case–control study from a prospective cohort of Ukrainian 3-year-old children was conducted. We evaluated predictors of elevated blood cadmium using a multivariable logistic regression model. The model included socioeconomic data, parent occupation, environmental tobacco smoke, hygiene, body-mass index, and diet. Dietary habits were evaluated using the 1992 Block-NCI-HHHQ Dietary Food Frequency survey. Elevated cadmium was defined as blood levels in the upper quartile (⩾0.25 μg/L). The mean age for all 80 children was 36.6 months. Geometric mean cadmium level was 0.21 μg/L (range=0.11–0.42 μg/L; SD=0.05). Blood cadmium levels were higher among children taking zinc supplements (0.25 vs 0.21 μg/L; P = 0.032 ), children who ate sausage more than once per week (0.23 vs 0.20; P = 0.007 ) and children whose fathers worked in a by-product coking industry (0.25 vs 0.21; P = 0.056 ). In the multivariable model, predictors of elevated blood cadmium levels included zinc supplementation (adjusted OR=14.16; P < 0.01 ), father working in a by-product coking industry (adjusted OR=8.50; P = 0.03 ), and low body mass index (<14.5; adjusted OR=5.67; P = 0.03 ). This is the first study to indicate a strong association between elevated blood cadmium levels and zinc supplementation in young children. Whole-blood cadmium levels observed in this group of Ukrainian children appear to be similar to those reported in other Eastern European countries.

Elevated Zinc Transporter-6 in Mild Cognitive Impairment, Alzheimer Disease, and Pick Disease

Filamentous cytoplasmic inclusions are hallmarks of Alzheimer disease (AD) and Pick disease (PD). Although previous studies show elevated zinc (Zn) in AD brain, there has been little study of zinc transporter (ZnT) proteins that are critical in the maintenance of Zn homeostasis. Using Western blot analysis, we show significantly elevated ZnT-6, the protein responsible for sequestration of Zn in the trans-Golgi network, in the hippocampus/parahippocampal gyrus (HPG) of AD subjects compared to age-matched controls and a trend toward elevated ZnT-6 in subjects with amnestic mild cognitive impairment (MCI). Based on these data, we used immunohistochemistry to investigate the cellular distribution of ZnT-6 in the HPG of control subjects and subjects with MCI, AD, and PD. Comparison of immediately adjacent serial sections stained using the modified Bielschowsky method and immunostained for ZnT-6 showed elevated ZnT-6 in 89 +/- 7% of neurofibrillary tangle (NFT)-bearing neurons in AD and 100 +/- 19% of Pick bodies in PD specimens. Confocal microscopy of HPG from MCI subjects double labeled for ZnT-6 and MC-1, a marker of early NFT formation, showed 85 +/- 4% of MC-1-positive cells were strongly ZnT-6-positive. Increased ZnT-6 immunostaining in neurons containing cytoplasmic inclusions in MCI, AD, and PD suggests a role for ZnT-6 in the pathogenesis of these lesions.

Mitochondrial aconitase and citrate metabolism in malignant and nonmalignant human prostate tissues

BackgroundIn prostate cancer, normal citrate-producing glandular secretory epithelial cells undergo a metabolic transformation to malignant citrate-oxidizing cells. m-Aconitase is the critical step involved in this altered citrate metabolism that is essential to prostate malignancy. The limiting m-aconitase activity in prostate epithelial cells could be the result of a decreased level of m-aconitase enzyme and/or the inhibition of existing m-aconitase. Earlier studies identified zinc as an inhibitor of m-aconitase activity in prostate cells; and that the depletion of zinc in malignant cells is an important factor in this metabolic transformation. However, a possibility remains that an altered expression and level of m-aconitase enzyme might also be involved in this metabolic transformation. To address this issue, the in situ level of m-aconitase enzyme was determined by immunohistochemical analysis of prostate cancer tissue sections and malignant prostate cell lines.ResultsThe immunocytochemical procedure successfully identified the presence of m-aconitase localized in the mitochondrial compartment in PC-3, LNCaP, and DU-145 malignant prostate cell lines. The examination of prostate tissue sections from prostate cancer subjects demonstrated that m-aconitase enzyme is present in the glandular epithelium of normal glands, hyperplastic glands, adenocrcinomatous glands, and prostatic intraepithelial neoplastic foci. Quantitative analysis of the relative level of m-aconitase in the glandular epithelium of citrate-producing adenomatous glands versus the citrate-oxidizing adenocarcinomatous glands revealed no significant difference in m-aconitase enzyme levels. This is in contrast to the down-regulation of ZIP1 zinc transporter in the malignant glands versus hyperplastic glands that exists in the same tissue samples.ConclusionThe results demonstrate the existence of m-aconitase enzyme in the citrate-producing glandular epithelial cells; so that deficient m-aconitase enzyme is not associated with the limiting m-aconitase activity that prevents citrate oxidation in these cells. The level of m-aconitase is maintained in the malignant cells; so that an altered enzyme level is not associated with the increased m-aconitase activity. Consequently, the elevated zinc level that inhibits m-aconitase enzyme is responsible for the impaired citrate oxidation in normal and hyperplastic prostate glandular epithelial cells. Moreover, the down-regulation of ZIP1 zinc transporter and corresponding depletion of zinc results in the increase in the activity of the existing m-aconitase activity in the malignant prostate cells. The studies now define the mechanism for the metabolic transformation that characterizes the essential transition of normal citrate-producing epithelial cells to malignant citrate-oxidizing cells.

A Mutation in Sec15l1 Disrupts the Transferrin Cycle and Causes Anemia in Hemoglobin Deficit (hbd) Mice.

Mouse mutants have been used to identify and characterize genes involved in iron homeostasis. The mouse mutant hemoglobin deficit (hbd), has inherited hypochromic, microcytic anemia and elevated zinc protoporphyrin in the setting of replete iron stores, consistent with a selective defect in erythroid iron assimilation. Circulating soluble transferrin receptor, a marker of iron-restricted erythropoiesis, is elevated out of proportion to the anemia. A mapping population of >3300 backcross animals allowed assignment of the hbd locus to a 0.5 Mb region on chromosome 19. Seven candidate genes were identified in mouse genome databases. Only Sec15l1, encoding one of two mouse homologs of yeast Sec15p, carried a mutation unique to hbd. The mutation deleted 4.5 kb of Sec15l1 genomic DNA including a 69 bp exon. Two distinct antibodies elicited against murine Sec15l1 demonstrated that there was little or no Sec15l1 protein detectable in tissues from hbd animals, suggesting that the mutant form was unstable in vivo. To confirm that mutation of Sec15l1 was responsible for the hbd phenotype, hbd bone marrow cells were transduced with a retrovirus expressing wild type Sec15l1 and transplanted into hbd mice. Expression of the wild type protein partially corrected the anemia. For further confirmation, mice carrying a different, targeted mutation in Sec15l1 were bred with hbd mice. Compound mutant mice carrying both the targeted and hbd alleles recapitulated the hbd phenotype. Sec15l1 functions as a component of the mammalian multi-protein exocyst complex. Previous studies in model organisms suggested that the exocyst is critical for a variety of cellular functions; loss of other exocyst proteins caused early lethality. We speculate that Sec15l2, a mammalian homolog of Sec15l1, can substitute in non-erythroid tissues. Expression analysis showed that little or no Sec15l2 was present in hbd spleen, which is massively infiltrated with erythroid precursors. The exocyst is an effector for Rab11, a GTPase involved in recycling of transferrin cycle endosomes. In S. cerevisiae, Sec15p interacts both with Sec10p, another exocyst component, and with a yeast homolog of Rab11. Preliminary studies suggest that the hbd form of mammalian Sec15l1, expressed in yeast, retains its ability to interact with both of its mammalian partner proteins - Rab11 and Sec10. We conclude that depletion of Sec15 in hbd mice alters transferrin receptor recycling and, possibly, enhances transferrin receptor shedding. As a consequence, erythroid iron assimilation is impaired. Sec15L1 should be considered a candidate gene in patients with inherited iron-resistant iron deficiency anemia.

Nm1054: a spontaneous, recessive, hypochromic, microcytic anemia mutation in the mouse

AbstractHypochromic, microcytic anemias are typically the result of inadequate hemoglobin production because of globin defects or iron deficiency. Here, we describe the phenotypic characteristics and pathogenesis of a new recessive, hypochromic, microcytic anemia mouse mutant, nm1054. Although the mutation nm1054 is pleiotropic, also resulting in sparse hair, male infertility, failure to thrive, and hydrocephaly, the anemia is the focus of this study. Hematologic analysis reveals a moderately severe, congenital, hypochromic, microcytic anemia, with an elevated red cell zinc protoporphyrin, consistent with functional erythroid iron deficiency. However, serum and tissue iron analyses show that nm1054 animals are not systemically iron deficient. From hematopoietic stem cell transplantation and iron uptake studies in nm1054 reticulocytes, we provide evidence that the nm1054 anemia is due to an intrinsic hematopoietic defect resulting in inefficient transferrin-dependent iron uptake by erythroid precursors. Linkage studies demonstrate that nm1054 maps to a genetic locus not previously implicated in microcytic anemia or iron phenotypes.

Zn2+Inhibits Mitochondrial Movement in Neurons by Phosphatidylinositol 3-Kinase Activation

Mitochondria have been identified as targets of the neurotoxic actions of zinc, possibly through decreased mitochondrial energy production and increased reactive oxygen species accumulation. It has been hypothesized that impairment of mitochondrial trafficking may be a mechanism of neuronal injury. Here, we report that elevated intraneuronal zinc impairs mitochondrial trafficking. At concentrations just sufficient to cause injury, zinc rapidly inhibited mitochondrial movement without altering morphology. Zinc chelation initially restored movement, but the actions of zinc became insensitive to chelator in <10 min. A search for downstream signaling events revealed that inhibitors of phosphatidylinositol (PI) 3-kinase prevented this zinc effect on movement. Moreover, transient inhibition of PI 3-kinase afforded neuroprotection against zinc-mediated toxicity. These data illustrate a novel mechanism that regulates mitochondrial trafficking in neurons and also suggest that mitochondrial trafficking may be closely coupled to neuronal viability.

Thiol and Metal Contents in Periphyton Exposed to Elevated Copper and Zinc Concentrations: A Field and Microcosm Study

Phytochelatins are metal-binding polypeptides produced by algae under metal exposure. The aim of this study was to investigate the effects of metal concentration variations in natural systems on periphyton at the biochemical level by analyzing its intracellular thiol content, in particular phytochelatins. To that purpose, two field campaigns were conducted in a stream subject to an increase of dissolved metal concentrations (particularly Cu and Zn) during rain events, which results in an increase of their accumulation in periphyton. At background metal concentrations, several thiols were detectable in periphyton, namely, glutathione (GSH), gamma-glutamylcysteine (gammaGluCys), phytochelatins (PC2), and some unidentified thiols, U1 and U2. Glutathione and gammaGluCys contents were found to vary independently of the rain, as well as U1 and U2, whereas the phytochelatin content increased during the rain events. To investigate whether Cu or Zn may be responsible for this increase, microcosm experiments were carried out with natural water enriched with Cu, Zn, and Cd separately, and Cu and Zn in combination. In this study, GSH, PC2, and U1 were also detected, but not gammaGluCys. An increase in accumulated Cu content did not induce any changes in thiol content, whereas an increase of the Zn content induced a decrease in GSH content and an increase in phytochelatin content. Zinc rather than Cu may thus induce a phytochelatin content increase in periphyton in the field studies. Addition of Cu and Zn in combination also induced an increase in phytochelatin content. Cadmium was found to be the most effective inducer, with the production of larger phytochelatins (PC3-4). This study is the first one to report changes in thiol content in periphyton in response to an increase of the metal concentration in natural freshwaters.

Heteromeric Protein Complexes Mediate Zinc Transport into the Secretory Pathway of Eukaryotic Cells

The cation diffusion facilitator (CDF) family of metal ion transporters plays important roles in zinc transport at all phylogenetic levels. In this report, we describe a novel interaction between two members of the CDF family in Saccharomyces cerevisiae. One CDF member in yeast, Msc2p, was shown recently to be involved in zinc transport into the endoplasmic reticulum (ER) and required for ER function. We describe here a newly recognized CDF family member in yeast, Zrg17p. ZRG17 was previously identified as a zinc-regulated gene controlled by the zinc-responsive Zap1p transcription factor. A zrg17 mutant exhibits the same zinc-suppressible phenotypes as an msc2 mutant, including an induction of the unfolded protein response in low zinc. Moreover, a significant fraction of the total Zrg17p protein appears to localize to the ER. Their common phenotypes and localization suggested that these two proteins function together to mediate zinc transport into the ER. Consistent with this hypothesis, Msc2p and Zrg17p physically interact with each other, as determined by co-immunoprecipitation. Therefore, we propose that Msc2p and Zrg17p form a heteromeric zinc transport complex in the ER membrane. We also demonstrate that ZnT5 and ZnT6, mammalian homologues of Msc2p and Zrg17p, functionally interact as well. These results suggest that heteromeric complexes formed by different CDF members may be a common phenomenon for this ubiquitous family of metal ion transporters.

Growth and Metal Accumulation of Mycorrhizal Sorghum Exposed to Elevated Copper and Zinc

Arbuscular mycorrhizal fungi (AMF) alter heavy metal acquisition by higher plants and may alter plant response to soil-contaminating heavy metals. Two communities comprised of Glomus intraradices and G. spurcum were investigated for their influence on copper (Cu) and zinc (Zn) resistance of Sorghum bicolor. One community was isolated from a Cu- and Zn-contaminated soil (AMF-C) and one consisted of isolates from non-contaminated soil (AMF-NC). Non-mycorrhizal (NM) sorghum plants were also included. The two community ecotypes differed in their capacity to protect sorghum from Cu and Zn toxicity and exhibited differential metal uptake into hyphae and altered heavy metal uptake by roots and translocation to plant shoots. AMF-C reduced Cu acquisition under elevated Cu conditions, but increased Cu uptake and translocation by sorghum under normal Cu conditions, patterns not exhibited by AMF-NC or NM plants. Hyphae of both fungal ecotypes accumulated high concentrations of Cu under Cu exposure. AMF-C exhibited elevated hyphal Zn accumulation and stimulated Zn uptake and translocation in sorghum plants compared to AMF-NC and NM plants. Differences in metal resistance between fungal treatments and between mycorrhizal and non-mycorrhizal plants were not related to differences in nutrient relations. The enhanced Cu resistance of sorghum and altered patterns of Cu and Zn translocation to shoots facilitated by AMF isolated from the metal-contaminated soil highlight the potential for metal-adapted AMF to increase the phytoremediation potential of mycotrophic plants on metal-contaminated environments.

Psittacine Plasma Concentrations of Elements: Daily Fluctuations and Clinical Implications

During the past 2 decades, the potential for excessive exposure of pet birds to zinc has become a concern for many pet bird owners. Ideally, avian zinc toxicosis is diagnosed on the basis of history of exposure to zinc, radiographic evidence of ingested metal, occurrence of melena, detection of an elevated plasma zinc concentration, and response to treatment. However, most pet birds suspected of having zinc toxicosis present with vague signs and lack of radiographic evidence; therefore, the diagnosis relies on the presence of an elevated plasma zinc concentration. A question was, is there a significant diurnal variation in the zinc concentration in psittacine birds and could this be clinically relevant? Because studies in other species have shown that zinc is not the only element that shows a diurnal variation, the authors examined 13 other plasma elements including arsenic, cadmium, calcium, cobalt, copper, iodine, iron, magnesium, manganese, molybdenum, potassium, selenium, and total phosphorus. Fifteen adult psittacine birds housed in the same aviary were used in this study. Three blood samples, separated by 4 hours, were taken from the right jugular vein in each bird. All elements were measured in plasma. Zinc, copper, and molybdenum revealed diurnal fluctuations. The results of this study suggest that interpretation of clinical samples may be more complicated than previously believed. Furthermore, on the basis of the results of this study, it is possible that some avian reference ranges may need to be reexamined.