Determination of zinc in biological samples by atomic absorption spectrometry

Combination of engineering the substrate and Ca2+ binding domains of heparinase I to improve the catalytic activity

Heparinase I (EC 4.2.2.7), is an enzyme that cleaves heparin, showing great potential for eco-friendly production of low molecular weight heparin (LMWH). However, owing to its poor catalytic activity and thermal stability, the industrial application of heparinase I has been severely hindered. To improve the catalytic activity, we proposed to engineer both the substrate and Ca2+ binding domains of heparinase I. Several heparinases I from different organisms were selected for multiple sequence alignment and molecular docking to screen the key residues in the binding domain. Nine single-point mutations were selected to enhance the catalytic activity of heparinase I. Among them, T250D was the most highly active one, whereas mutations around Ca2+ binding domain yielded two active mutants. Mutant D152S/R244K/T250D with significantly increased catalytic activity was obtained by combined mutation. The catalytic efficiency of the mutant was 118,875.8 min-1·µM-1, which was improved 5.26 times. Molecular modeling revealed that the improved activity and stability of the mutants were probably attributed to the formation of new hydrogen bonds. The highly active mutant had great potential applications in industry and the strategy could be used to improve the performance of other enzymes.

Novel Thermostable Heparinase Based on the Genome of Bacteroides Isolated from Human Gut Microbiota

Among the nutrients available to the human gut microbiota, the complex carbohydrates and glycosaminoglycans are important sources of carbon for some of the species of human gut microbiota. Glycosaminoglycan (heparin) from the host is a highly preferred carbohydrate for Bacteroides. To explore how gut microbiota can effectively use heparin as a carbon source for growth, we conducted a screening of the Carbohydrate-Active enzymes (CAZymes) database for lytic enzymes of the PL13 family and Research Center of Food Biotechnology at School of Food Science and Technology of Jiangnan University database of Bacteroides to identify novel glycosaminoglycan-degrading bacterial strains. Four Bacteroides species (Bacteroides eggerthii, Bacteroides clarus, Bacteroides nordii, and Bacteroides finegoldii) that degraded heparin were selected for further studies. Analysis of the polysaccharide utilization sites of the four strains revealed that all of them harbored enzyme encoding genes of the PL13 family. Functional analysis revealed the activity of CAZymes in a medium containing heparin as the sole carbon source, suggesting their potential to degrade heparin and support growth. The four enzymes were heterologous expressed, and their enzymatic properties, kinetics, and thermal stability were determined. The lytic enzyme of B. nordii had high enzymatic activity and thermal stability. The features that cause this high thermal stability were elucidated based on an examination of the three-dimensional structure of the protein. Our findings provide an important theoretical basis for the application of glycosaminoglycans and glycosaminoglycan-degrading enzymes in the medical and biotechnology industries, and an important scientific basis for precision nutrition and medical intervention studies using gut microbiota or enzymes as targets.

The lysosome among targets of metformin: new anti-inflammatory uses for an old drug?

BACKGROUND

Rheumatoid arthritis and type-2 diabetes exhibit progressive co-morbidity. Chloroquine (CQ) reportedly improves both. CQ inhibits lysosomal function in cultured cells at supra-therapeutic concentration; however, this is doubted as target mechanism. Some anti-diabetic biguanides are metal-interactive lysosomal inhibitors; and all bind Zn(2+).

OBJECTIVES

i) To bioassay the potency of CQ using (3)H-leucine release from perfused myocardial tissue. ii) To determine whether metformin (MET) is CQ-mimetic, and interactive with Zn(2+).

RESULTS

Therapeutic CQ concentration (0.1 - 0.5 microM) clearly does cause lysosomal inhibition although delayed and submaximal. MET alone (10 microM) caused sub-maximal inhibition. Supra-physiological extracellular Zn(2+) (5 - 50 microM) alone increased tissue Zn(2+) content, and inhibited lysosomal proteolysis. Physiological equivalent Zn(2+) (approximately 1 microM) had no effect. MET (<or= 25 microM) and Zn(2+) (<or= 1 microM) exhibited astounding 10 - 100 fold anti-lysosomal synergy. Cathepsin B was 50% inhibited by 1 muM Zn(2+), and is reportedly inhibited by gold agents.

INTERPRETATION

MET somehow increases the natural inhibitory action of action of Zn(2+) against cysteinyl proteases. TNF-alpha activates lysosomal function; and CatB is among post-receptor players. MET might decrease antigen processing in specialized cells, and lysosomal hyper-catabolism in other cells.

CONCLUSIONS

Trials of MET for new use as an anti-inflammatory agent are suggested. Guanidylguanidine is a practical pharmacophore for synthesis of future anti-lysosomal agents.

An innovative continuous flow system for monitoring heavy metal pollution in water using transgenic Xenopus laevis tadpoles

While numerous detection methods exist for environmental heavy metal monitoring, easy-to-use technologies combining rapidity with in vivo measurements are lacking. Multiwell systems exploiting transgenic tadpoles are ideal but require time-consuming placement of individuals in wells. We developed a real-time flow-through system, based on Fountain Flow cytometry, which measures in situ contaminant-induced fluorescence in transgenic amphibian larvae immersed in water samples. The system maintains the advantages of transgenic amphibians, but requires minimal human intervention. Portable and self-contained, it allows on-site measurements. Optimization exploited a transgenic Xenopus laevis bearing a chimeric gene with metal responsive elements fused to eGFP. The transgene was selectively induced by 1 microM Zn(2+). Using this tadpole we show the continuous flow method to be as rapid and sensitive as image analysis. Flow-through readings thus accelerate the overall process of data acquisition and render fluorescent monitoring of tadpoles suitable for on-site tracking of heavy metal pollution.

On the origin of life in the zinc world. 2. Validation of the hypothesis on the photosynthesizing zinc sulfide edifices as cradles of life on Earth

BACKGROUND

The accompanying article (A.Y. Mulkidjanian, Biology Direct 4:26) puts forward a detailed hypothesis on the role of zinc sulfide (ZnS) in the origin of life on Earth. The hypothesis suggests that life emerged within compartmentalized, photosynthesizing ZnS formations of hydrothermal origin (the Zn world), assembled in sub-aerial settings on the surface of the primeval Earth.

RESULTS

If life started within photosynthesizing ZnS compartments, it should have been able to evolve under the conditions of elevated levels of Zn2+ ions, byproducts of the ZnS-mediated photosynthesis. Therefore, the Zn world hypothesis leads to a set of testable predictions regarding the specific roles of Zn2+ ions in modern organisms, particularly in RNA and protein structures related to the procession of RNA and the "evolutionarily old" cellular functions. We checked these predictions using publicly available data and obtained evidence suggesting that the development of the primeval life forms up to the stage of the Last Universal Common Ancestor proceeded in zinc-rich settings. Testing of the hypothesis has revealed the possible supportive role of manganese sulfide in the primeval photosynthesis. In addition, we demonstrate the explanatory power of the Zn world concept by elucidating several points that so far remained without acceptable rationalization. In particular, this concept implies a new scenario for the separation of Bacteria and Archaea and the origin of Eukarya.

CONCLUSION

The ability of the Zn world hypothesis to generate non-trivial veritable predictions and explain previously obscure items gives credence to its key postulate that the development of the first life forms started within zinc-rich formations of hydrothermal origin and was driven by solar UV irradiation. This concept implies that the geochemical conditions conducive to the origin of life may have persisted only as long as the atmospheric CO2 pressure remained above ca. 10 bar. This work envisions the first Earth biotopes as photosynthesizing and habitable areas of porous ZnS and MnS precipitates around primeval hot springs. Further work will be needed to provide details on the life within these communities and to elucidate the primordial (bio)chemical reactions.

REVIEWERS

This article was reviewed by Arcady Mushegian, Eugene Koonin, and Patrick Forterre. For the full reviews, please go to the Reviewers' reports section.

The descrease of the in vitro proliferative response of zinc-treated stressed mice's thymic lymphocytes

Prolonged stimulation of newborn mice by intraperitoneal injections with inactivated staphylococci induces a chronic neonatal inflammatory reaction and an associated oxidative-stress response. The chronically stimulated animals exhibit anorexy. show a reduction in their body weight and undergo a depression in both antibody synthesis andin vitro proliferativc response of Con A-stimulated splenic T-lymphocytes. These stressed animals also develop adrenal hyperplasia, hypozincamia and thymic hypoplasia. Despite this stress-mediated thymic involution, Con-A stimulated T-lymphocytes from thymus displayed increased theirin vitro proliferative response. Results of the present work show that intramuscular injections of zinc acetate in stressed mice, one single dose (5 microg) every other day for two weeks, reduce both the zinc concentration in the thymus gland and thein vitro proliferative response of their Con A-stimulated T-lymphocytes. The results suggest that prophylactic administration of zinc can have benefical consequences on the immunity of chronically stressed mice.

Post-Therapy Profile of Serum Total Cholesterol, Retinol and Zinc in Pediatric Acute Lymphoblastic Leukemia and Non-Hodgkin's Lymphoma

OBJECTIVE

To assess serum albumin, total cholesterol, retinol, zinc and hemoglobin in children who had completed treatment for acute lymphoblastic leukemia (ALL) and Non-Hodgkin's lymphoma (NHL).

METHODS

The above parameters were analyzed in 105 ALL and NHL and 108 age and sex-matched controls. Serum albumin, serum cholesterol and hemoglobin were estimated by colorimetric methods. Serum retinol was estimated by HPLC and serum zinc was estimated by atomic emission spectrophotometer (ICP-AES). Comparisons were made to stage of treatment (maintenance 6 with post-therapy), type of treatment (chemotherapy and radiation with only chemotherapy) and type of malignancy (ALL with NHL).

RESULTS

Only serum albumin in patients included at Maintenance(6) was significantly higher (t = 2.31, p = 0.05) than post-therapy patients. No significant difference in serum values was observed by type of treatment. Only total cholesterol was significantly higher in NHL patients than in ALL patients (t = 1.954, p = 0.05). Patients had comparable serum levels to that of controls. However, in patients and controls more than 75% children had deficient serum retinol levels, (< than 0.6989 micromol/l, or 20 microg/dl). Further, 75% patients and 54.7% controls had serum retinol levels less than 0.3439 micromol/l or 10 microg/dl.

CONCLUSION

The results of the present study indicate that cancer and its treatment did not have any long-lasting effect on serum albumin, total cholesterol, retinol, zinc and hemoglobin. Majority of subjects had low serum retinol suggestive of depleted liver reserves. The deficient serum retinol levels (< than 0.6989 micromol/l, or 20 microg/dl) in at least 75% of the patients and controls probably reflect poor dietary intake. A higher percentage of patients with low serum retinol levels may also be attributed to the possibility of urinary losses of retinol that occur during episodes of infection while on immunosuppressive anti-cancer drug therapy.

Binding of chimeric metal-binding green fluorescent protein to lipid monolayer

Membrane-based bioanalytical devices for metal determination using green fluorescent protein as the sensor molecule may be a useful future biomimetic material. However, in order to develop such a device, it is necessary first to understand the interaction of the protein with lipid membranes. Thus we have investigated the interaction between chimeric cadmium-binding green fluorescent proteins (CdBPGFPs) and lipid monolayers, using a film-balance technique complemented with epifluorescence microscopy. The binding avidity was monitored from the surface pressure vs. area isotherms or from the measured increase in the lateral pressure upon injection of the chimeric CdBPGFPs beneath the lipid monolayer. Increased fluidization as well as expansion of the surface area were shown to depend on the concentration of the CdBPGFPs. The kinetics of the protein-induced increase in lateral pressure was found to be biphasic. The chimeric CdBPGFPs possessed high affinity to the 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayer with a dissociation constant of Kd = 10(-8)M. Epifluorescence measurements showed that this affinity is due to the presence of the Cd-binding peptide, which caused the GFP to incorporate preferentially to the liquid phase and defect part of the rigid domain at low interfacial pressure. At high compression, the Cd-binding peptide could neither incorporate nor remain in the lipid core. However, specific orientation of the chimeric CdBPGFPs underneath the air-water interface was achieved, even under high surface pressure, when the proteins were applied to the metal-chelating lipid-containing surfaces. This specific binding could be controlled reversibly by the addition of metal ions or metal chelator. The reversible binding of the chimeric CdBPGFPs to metal-chelating lipids provided a potential approach for immobilization, orientation and lateral organization of a protein at the membrane interface. Furthermore, the feasibility of applying the chelator lipids for the codetermination of metal ions with specific ligands was also revealed. Our finding clearly demonstrates that a strong interaction, particularly with fluid lipid domains, could potentially be used for sensor development in the future.

A survey of methods of analysis for minerals in feedstuffs

A wide range of minerals occurs in feedstuffs as naturally occurring and purposely added elements, as well as by adventitious contamination. These mineral elements can generally be classified as nutritionally essential major elements, nutritionally essential minor and trace elements, and those regarded as toxic or with an essential/toxic duality. A survey is presented of methods used for the determination of major, minor, and trace elements in feedstuffs and related biological materials. Currently available methods include the following: atomic absorption spectrometry, atomic emission spectrometry, mass spectrometry, neutron activation analysis, x-ray emission spectrometry, molecular light absorption spectrometry, molecular fluorometry, electrochemistry, Kjeldahl method (nitrogen), combustion elemental analysis, volumetry, ion chromatography, and gravimetry. Available reference, routine, official, unofficial, and recommended methods are reviewed as a basis for recommendations of methods most suitable for feedstuffs.

Changes in zinc, copper and metallothionein contents during oocyte growth and early development of the teleost Danio rerio (zebrafish)

In the present report, we investigated zinc, copper and metallothionein (MT) contents in zebrafish oocytes and embryos. Our results demonstrate that the metal content increases during oocytes maturation. Zinc increases from 30 ng/oocyte (stage-1 oocytes) to 100 ng/oocyte (stage-3 oocytes); copper varied from 1 ng/oocyte (stage-1 oocytes) to 3.5 ng/oocyte (stage-3 oocytes). During embryogenesis, zinc and copper contents dramatically increase after fertilisation around the 512-cells stage, then slowly decrease until the mid-gastrula stage. During oocyte growth, the changes in the MT level are proportional to metal content, whereas during embryogenesis the pattern of MT accumulation does not parallel that of the two metals. Indeed, the maternal pool of MT decreases steadily during the early stages of the development until the gastrula stage. We have examined the effect of cadmium on the expression of MT during zebrafish development. After cadmium exposure, MT content increases in embryos at the blastula stage, whereas no induction occurs in embryos at the gastrula stage. However, pre-treatment of embryos at the gastrula stage with 5-aza-2'-deoxycytidine induces MT synthesis following exposure to cadmium. These observations show that changes in metal levels are not correlated to MT content in the embryo, whereas DNA methylation is one of the factors regulating MT expression.

Optic nerve changes in zinc-deficient rats

In this study the optic nerve changes in zinc (Zn)-deficient rats are examined. Zinc is one of the essential trace elements and is known to be related to optic nerve diseases such as ethambutol neuropathy. However, the effect of Zn on the optic nerve has not been studied experimentally in animals. We used 3 week old weanling male Wistar Kyoto rats weighing 40-50 g. Rats were fed a Zn-deficient diet containing 0.007 mg of Zn per 100 g, all other nutrients and distilled and deionized water. The same water supplemented with 3 mg Zn per 100 g was given to the control group. After 4 or 7 weeks on a Zn-deficient diet, the optic nerve was examined with an electron microscope. A recovery group was fed a Zn-containing diet for 5 weeks after 7 weeks on the Zn-deficient diet. The serum Zn levels of the deficient group were significantly decreased at both 4 and 7 weeks. Most of the Zn-deficient rats showed hair loss around the eyes and on the extremities. Ultrastructural findings were as follows. The number of myelinated axons of Zn-deficient rats at 4 and 7 weeks were significantly decreased and the myelin sheaths were significantly thinner in the Zn-deficient groups and in the recovery group. Unmyelinated axons were more numerous than in the control rats. Destruction of myelin and proliferation of glial cells were found in the optic nerves of Zn-deficient rats. This study suggests that the optic nerve needs Zn for the maintenance of its cell structure and even if Zn is supplied to the Zn-deficient rats, destruction of the myelin structure may continue. Zn-deficiency induce a decrease of myelinated nerve fibers, and it is thought that optic neuropathy in patients treated with some drugs such as ethambutol may be a secondary change due to Zn-deficiency following drug administration.

Actions and interactions of thyroid hormone and zinc status in growing rats

Both thyroid hormone (triiodo-L-thyronine, T3) and zinc play important roles in growth and development. The T3 receptor is thought to require zinc to adopt its biologically active conformation. Some of the effects of zinc deficiency, therefore, may be due to loss of zinc from the T3 receptor and impairment of T3 action. This possibility was investigated in growing rats by examining the effects of hypothyroidism and hyperthyroidism in zinc-deficient, pair-fed and control rats. Measurement of serum zinc and T3 confirmed the efficacy of the treatments. Zinc deficiency and hypothyroidism resulted in lower food intake and growth failure, but no interaction was observed between the two treatments. Individual tissue weights were influenced by thyroid status as expected, regardless of zinc status. Both dietary and hormonal treatments influenced serum insulin-like growth factor (IGF)-I in an interactive manner. IGF-I was reduced to a greater extent in zinc-deficient than in pair-fed rats compared with controls. Both hypothyroidism and hyperthyroidism reduced serum IGF-I, and a greater reduction due to hyperthyroidism was apparent in zinc-deficient rats. IGF binding proteins were also influenced by diet and thyroid status. The hepatic expression of mRNA S14 was assessed as a direct index of the nuclear action of T3, but its response was not influenced by dietary treatment. Although confirming the role of both T3 and zinc in the regulation of growth and the somatotrophic axis, the growth failure of zinc deficiency does not appear to be due to impaired T3 function.

Zinc-induced hyperleptinemia relates to the amelioration of sucrose-induced obesity with zinc repletion

OBJECTIVE

Dietary zinc repletion can ameliorate sucrose-induced obesity. A positive correlation between zinc and leptin has been recently noted, and both are known as important mediators in appetite control. In this study, we examined whether the reported amelioration of sucrose-induced obesity by zinc repletion was consequent on the changes in circulating leptin levels.

RESEARCH METHODS AND PROCEDURES

Mice with obesity that was induced by giving a 32% sucrose solution in addition to a semipurified diet were divided into two groups based on whether they had 20 mg/liter zinc supplementation in their drinking water.

RESULTS

As expected, the mice with sucrose-induced obesity had hyperglycemia, hyperinsulinemia, hypertriglyceridemia, hyperleptinemia, and hypozincemia when compared with the mice given the diet alone. Body weight gain, body fat content, and food and sucrose intake tended to decrease but not with statistical significance in sucrose-fed obese mice with zinc supplementation. Nevertheless, some serum variables (glucose, insulin, triglycerides, and zinc) in sucrose-fed obese mice with zinc treatment were approximate to those values of the mice given the diet alone. Moreover, sucrose-fed obese mice with zinc supplementation had the highest serum values of leptin.

DISCUSSION

This study indicates that the amelioration of sucrose-induced obesity by zinc repletion may be partly attributable to the hyperleptinemia induced by the mineral.

Physical characterization of plakophilin 1 reconstituted with and without zinc

Plakophilin 1 (PKP1) belongs to the arm-repeat protein family which is characterized by the presence of a conserved 42-amino-acid motif. Despite individual members of the family containing a similar type of structural domain, they exhibit diverse cellular functions. PKP1 is ubiquitously expressed in human tissues and, depending on the type of cell, found prominently in the karyoplasm and/or in desmosomes. In surface plasmon resonance detection experiments, we noticed that PKP1 specifically bound zinc but not calcium or magnesium. Therefore we have used circular dichroism spectroscopy, limited proteolysis, analytical ultracentrifugation, electron microscopy and dynamic light scattering to establish the physical properties of recombinant PKP1 depending on the presence or absence of zinc. The alpha helix content of PKP1 was considerably higher when reconstituted with zinc than without. By atomic absorption spectroscopy 7.3 atoms zinc were shown to be tightly associated with one molecule of wild-type PKP1. The zinc-reconstituted protein formed globular particles of 21.9 +/- 8.4 nm diameter, as measured by electron microscopy after glycerol spraying/rotary metal shadowing. In parallel, the average sedimentation coefficient (s20, w) for zinc-containing PKP1 was 41S and its diffusion coefficient, as obtained by dynamic light scattering, 1.48 x 10-7 cm2.s-1. The molecular mass of 2.44 x 106 obtained from s and D yields an average stoichiometry of 30 for the PKP1 oligomer. In contrast, PKP1, reconstituted without zinc, contained no significant amount of zinc, sedimented with 4.6S, and was present in monomeric form as determined by sedimentation equilibrium centrifugation.

Xenopus laevis embryo development: arrest of epidermal cell differentiation by the chelating agent 1,10-phenanthroline

The embryonic epidermis of stage 35 Xenopus laevis embryos is a highly differentiated structure composed of four cell types arranged in a regular architecture. Each type is distinguished by its distinct morphological characteristics. Some cells are ciliated (type 1); others have their surfaces covered by abundant, secreted vesicles of 0.1 microm diameter (type 2), or multiple linear aggregates of spherical subunits on their apical surfaces (type 3) or large secreted vesicles that emanate from prominent apical holes of 1 microm diameter (type 4). In contrast, the macroscopic appearance of embryos exposed to 10 microM 1,10-phenanthroline (OP) as well as the ultramicroscopic structure and organization of their epidermal cells are markedly altered. The most predominant cells of the embryonic epidermis are undifferentiated and of heterogeneous size. They lack any characteristic morphology and are arranged irregularly. Ghost cells are also identified. The recognizable differentiated cells are decreased in number and present in a scattered arrangement. These are identified as either type 1 or 2 cells but with ciliae that are shorter and thicker than control or with only a few vesicles larger than 0.1 microm in diameter on their surface. No cells with linear aggregates or prominent apical holes are identified. Except for the altered epidermis, the embryos do not develop any other major organs and exhibit axial abnormalities with an average dorso-anterior index of three. Thus, the chelating agent OP perturbs metal dependent processes essential for terminal differentiation that may likely account for the resultant abnormalities of embryo organogenesis and morphogenesis.

AtMSI4 and RbAp48 WD-40 repeat proteins bind metal ions

The mammalian RbAp48 protein is the most extensively studied member of the conserved family of Msi1-like WD-40 repeat proteins, which are components of complexes involved in the assembly and modification of chromatin. We have isolated a plant homolog of RbAp48, AtMSI4. By metal affinity chromatography, zinc blotting and atomic absorption analysis, we demonstrate that purified recombinant RbAp48 and AtMSI4 proteins bind 3-4 metal ions per molecule of protein. Metal competition assays indicate a preference for zinc. Both N- and C-terminal halves of RbAp48 and AtMSI4 display zinc binding activity, suggesting it is an intrinsic property of the propeller structures likely to be formed by these proteins. Metal binding might mediate and/or regulate protein-protein interactions which are functionally important in chromatin metabolism.

Effects of zinc supplementation on the plasma glucose level and insulin activity in genetically obese (ob/ob) mice

The effects of zinc supplementation (20 mM ZnCl2 from the drinking water for eight weeks) on plasma glucose and insulin levels, as well as its in vitro effect on lipogenesis and lipolysis in adipocytes were studied in genetically obese (ob/ob) mice and their lean controls (+/?). Zinc supplementation reduced the fasting plasma glucose levels in both obese and lean mice by 21 and 25%, respectively (p < 0.05). Fasting plasma insulin levels were significantly decreased by 42% in obese mice after zinc treatment. In obese mice, zinc supplementation also attenuated the glycemic response by 34% after the glucose load. The insulin-like effect of zinc on lipogenesis in adipocytes was significantly increased by 80% in lean mice. However, the increment of 74% on lipogenesis in obese mice was observed only when the zinc plus insulin treatment was given. This study reveals that zinc supplementation alleviated the hyperglycemia of ob/ob mice, which may be related to its effect on the enhancement of insulin activity.

Zinc attenuation of GDP binding to brown adipocytes mitochondria in genetically obese (ob/ob) mice

In this study, we investigate the in vitro effect of zinc addition on guanosine diphosphate (GDP) binding to mitochondria in brown adipocytes of genetically obese (ob/ob) mice. Interscapular brown adipocytes of male mice (obese; lean) at 4 and 12 wk of age were incubated with 0, 50, 100, or 200 microM zinc sulfate. Mitochondria were then isolated and their GDP binding capacities were measured. The GDP-binding capacities of ob/ob mice were lower than lean mice, with or without zinc addition, in both age groups (p < 0.05). Zinc addition did not have any significant effect on GDP binding in lean mice. GDP binding decreased with increasing zinc addition in ob/ob mice, and this attenuation was more predominant in 12-wk old ob/ob mice. Moreover, we found that high magnesium addition (5 mM) increased GDP binding in lean mice, but this effect was not significant in ob/ob mice. This study reveals that brown adipose tissue thermogenesis in ob/ob mice could be greatly attenuated by zinc addition, suggesting that zinc may play a regulatory role in obesity.

Endogenous zinc concentrations in cysteamine-induced duodenal ulcers in the rat

Exogenously administered zinc compounds have been shown to possess anti-ulcer activity against a wide variety of ulcerogenic agents, both in laboratory animal models and in human peptic ulcer disease. However, a strong possibility exists that endogenous zinc may also play an important role during noxious events by various mechanisms. Therefore, the aim of this study was to focus on the changes of endogenous zinc serum and tissue concentrations in cysteamine-induced duodenal lesions. We used atomic absorption spectrophotometry to determine the tissue and serum concentrations of zinc in normal (control) rats and those with cysteamine-induced duodenal ulcers. The results obtained in this study indicated that the onset, development and spontaneous healing of ulcer lesions were associated with certain shifts in zinc serum and tissue concentrations. Prior to ulcer formation, a significant increase was noted in serum zinc values. With the onset of duodenal lesions, zinc serum concentrations significantly decreased, while there was a significant increase in duodenal tissue concentrations when compared to healthy control animals. Zinc tissue concentrations decreased and returned to starting values by the end of the first week of spontaneous healing. This decrease in zinc tissue concentration corresponded to the healing rate of the duodenal ulcers. Serum zinc concentrations also returned to starting values within the first week period. These observations indicate and confirm that zinc could play an important role in duodenal ulcer disease and represent a natural defense system in the body.

Total body zinc depletion and its relationship to the development of hyperprolactinemia in chronic renal insufficiency

Modulation of free plasma zinc levels has been implicated in the increase in plasma prolactin levels seen in patients with chronic renal insufficiency (CRI). The relative importance of this mechanism in comparison to others, however, has not been elucidated. Zinc equilibrium between plasma and red blood cells is partly dependent upon red blood cell carbonic anhydrase (CA). In the present paper, we have investigated the interrelationships among total plasma zinc, leukocyte zinc, prolactin, and erythrocyte CA in patients with CRI. Uremic patients were shown to have significantly increased levels of plasma prolactin and erythrocyte CA activity when compared to normal controls. Moreover, red blood cell CA total concentration and isoenzyme-I and-II levels, as well as plasma zinc were found to be significantly decreased in uremic patients in comparison to normal controls. In patients with CRI, a negative correlation was demonstrated between erythrocyte CA catalytic activity and plasma zinc, as well as between plasma zinc and plasma prolactin levels. Moreover, leukocyte zinc content, which is a reliable indicator of total body zinc stores, was found to be significantly decreased in uremic patients when compared to normal controls. A strong negative correlation between leukocyte zinc content and plasma prolactin levels was documented in CRI patients. Our results suggest that alterations in erythrocyte CA levels, enzymatic activity or isoenzyme profile are most probably mechanistically and etiologically unrelated to the high plasma prolactin levels in CRI patients. Contrariwise, depletion of total body zinc stores, rather than redistribution of this trace metal among extracellular compartments, may represent one of the major contributing mechanisms leading to uremic hyperprolactinemia.

Zinc supplementation aggravates body fat accumulation in genetically obese mice and dietary-obese mice

A perturbation of zinc metabolism has been noted in numerous laboratory animals with diabetes and obesity. The effects of zinc supplementation on body fat deposition in two types of experimental obese mice: genetically obese (ob/ob) mice and high-fat diet-induced ICR obese (HF) mice were investigated in this study. Their lean controls were +/? mice, and ICR on basal diet, respectively. The mice in the zinc-supplemented groups were administered 200 mg/kg zinc in their diets for 6 wk. Both the ob/ob mice and the HF mice, that were fed a diet containing a marginal zinc dosage (4-6 mg/kg), had lower zinc levels in their serum and carcass, and higher body fat content than their respective lean controls (p < 0.01). After zinc supplementation, ob/ob mice and the HF mice significantly (p < 0.05) increased their body fat by 49.4% and 18.9%, respectively. This study revealed that body fat deposition can be aggravated by zinc supplementation in both types of obese mice. Zinc may be associated with the energy homeostasis of obesity, via its interaction with dietary fat consumption.

Zinc, iron, and copper contents of Xenopus laevis oocytes and embryos

Zinc is essential for vertebrate development; its deficiency results in multiple congenital malformations. Knowledge of the zinc biochemistry that underlies embryologic development is very limited. This has led us to investigate the zinc, iron, and copper contents of Xenopus laevis oocytes and embryos. Stage 1-6 oocytes, isolated from ovaries, and stage 1-40 embryos, obtained by in vitro fertilization techniques, were washed in metal-free water prior to digestion by 70% ultrapure HNO3. The metal content of the digests was analyzed by atomic absorption spectrometry. Stage 6 oocytes contain 65.8 +/- 4, 31.1 +/- 3, and 0.68 +/- 0.2 ng of zinc, iron and copper, respectively. The corresponding concentrations are 1, 0.5, and 0.01 mM in 1 microliter eggs. The metal content varies as a function of egg maturation. The zinc content increases from 3-7 to > 60 ng by stages 3 and 6, respectively. A similar pattern is noted for iron, which increases from 2-5 to 30 ng at analogous stages. In contrast, the copper content remains virtually unchanged in oocytes undergoing maturation. Importantly, the total of all three metals does not vary throughout the first 50 stages of development, when all tadpole organs are forming. Hence, the full complement of zinc, iron, and copper needed for incorporation into apoproteins during development is already present at a time when oocyte maturation is completed. The specific metalloproteins that store, donate, and accept these metals during induction and organogenesis and the alterations caused by metal deficiency can now be identified.

Phenylalaninylargininylarginine: a novel tripeptide exerting Zn(2+)-dependent, insulin-mimetic inhibitory action on myocardial proteolysis

A novel tripeptide, Phe-Arg-Arg, was found to exert a potent, insulin-mimetic inhibitory action on lysosomal proteolysis in the Langendorff-perfused rat heart. This tripeptide was synthesized based upon its partial structural analogy to the biguanide anti-hyperglycaemic agent, phenformin (phenylethylbiguanide), which has previously been found to exert a Zn(2+)-dependent inhibitory action on lysosomal proteolysis. Hearts were biosynthetically labelled with [3H]leucine in vitro. The percentage change in subsequent release of [3H]leucine (2 mM non-radioactive leucine) was determined in non-recirculating perfusate. The background Zn2+ content of the perfusate was determined to be 20 nM. Major endogenous Zn2+ buffers were present in molar excess of Zn2+: 0.1 mM citrate, 0.2% BSA, and complete physiological amino acids. Infusion of maximally effective levels of chloroquine (30 microM) or insulin (5 nM) caused a 38% inhibition of total proteolysis, which corresponds to the lysosomal subcomponent. In the presence of background levels of perfusate Zn2+ the infusion of Phe-Arg-Arg (10 microM), insulin (5 nM), or phenformin (2 microM) maximally caused a 39% inhibition of [3H]leucine release. Combined infusion of maximally effective levels of insulin and Phe-Arg-Arg, or maximal levels of chloroquine and Phe-Arg-Arg did not cause additive inhibition of [3H]leucine release greater than the 39% inhibition caused by either agent alone, regardless of the order of infusion. Addition of physiological concentrations of Zn2+ (1 microM) to the background perfusate Zn2+ accelerated the insulin-mimetic action of submaximally effective levels of Phe-Arg-Arg, and increased its potency. Prior chelation of background Zn2+ by a 3 h perfusion with CaNa2 EDTA (2 microM) reversibly delayed the time course of Phe-Arg-Arg action and decreased its potency at submaximal concentrations.

A Euglena gracilis zinc endonuclease

A 26-kDa endonuclease has been purified to homogeneity from zinc-sufficient Euglena gracilis. The protein binds to single-stranded DNA with a higher affinity than to double-stranded DNA, but it exhibits nucleolytic activity toward both. Thus, it converts supercoiled plasmid pBR322 DNA into the linear form, a property characteristic of endonucleases, and it continues to act on the linearized DNA until it is completely degraded. It also hydrolyzes heat-denatured, single-stranded calf thymus DNA. Moreover, at amounts below 1 microgram, it enhances RNA synthesis by RNA polymerase II, a characteristic observed with other DNases. Its addition to an in vitro transcription assay increases RNA synthesis up to 3-fold. The nuclease requires two metal components to carry out its enzymatic activities. It hydrolyzes DNA only in the presence of millimolar amounts of magnesium or micromolar quantities of other activating metal ions, such as manganese, zinc, or cobalt. However, even when optimal concentrations of Mg2+ are present, micromolar amounts of the metal-chelating agents OP and HQSA completely inhibit pBR322 digestion. Transcription enhancement is also inhibited completely by both chelators at concentrations that do not affect the intrinsic polymerase II activity. By atomic absorption spectrometry, the enzyme contains 1 g-atom of Zn/mol, which is the likely target of chelator action. The nuclease protein can also be isolated from zinc-deficient E. gracilis, but remarkably it then contains 1 mol of Cu/g-atom and no zinc.(ABSTRACT TRUNCATED AT 250 WORDS)

The interactions of zinc, nickel, and cadmium with Xenopus transcription factor IIIA, assessed by equilibrium dialysis

Transcription factor IIIA (TFIIIA) was isolated from Xenopus ovary and treated with 1,10-phenanthroline to remove zinc. The interactions of apoTFIIIA with Zn2+, Ni2+, and Cd2+ were studied by equilibrium dialysis under anaerobic conditions (pH 7.0, 25 degrees C), using 65ZnCl2, 63NiCl2, and 109CdCl2 as the radioligands. The data for binding of Zn2+, Ni2+, and Cd2+ to apoTFIIIA were best-fitted by a model with two classes of binding sites. For Zn2+, the apparent dissociation constants (KdlZn and Kd2Zn) for the high- and low-affinity sites were 1.0 x 10(-8) and 2.6 x 10(-5) M; the apparent binding capacities of the two classes were 0.8 +/- 0.5 and 9.6 +/- 0.3 g-atoms of Zn/mol; the Hill coefficient was 1.18, consistent with positive cooperativity of Zn-binding sites. For Ni2+, the apparent KdlNi and Kd2Ni values were 2.3 x 10(-5) and 5.2 x 10(-4) M; the apparent binding capacities were 2.3 +/- 0.6 and 8.6 +/- 0.6 g-atoms of Ni/mol; the Hill coefficient was 1.20, consistent with positive cooperativity of Ni-binding sites. For Cd2+, the apparent KdlCd and Kd2Cd values were 2.8 x 10(-6) and 1.6 x 10(-4) M; the apparent binding capacities were 0.9 +/- 0.3 and 2.4 +/- 0.5 g-atoms of Cd/mol; the Hill coefficient was 0.53, consistent with negative cooperativity or heterogeneity of Cd-binding sites. This study has the following significance: First, it helps to resolve a controversy about the zinc content of purified TFIIIA. Second, it shows that the KdlZn of apoTFIIIA is less than the reported KdZn of thionein, consistent with the hypothesis that thionein modulates gene expression by competing with TFIIIA and other Zn-finger proteins for intracellular Zn2+ stores. Third, it confirms previous indirect evidence that the affinity of apoTFIIIA for Zn2+ is much greater than for Cd2+, and that the affinity for Cd2+ is greater than for Ni2+.