The effects of cropping corn on the extractability of zinc added to a calcareous soil

The effects of cropping corn on the decrease in the extractability of Zn added to a calcareous soil were studied by a pot experiment and chemical extractions. The results show that the concentrations of Zn exchangeable with MgCl₂ (EXC-Zn) and extractable with DTPA (DTPA-Zn) in the soils with added Zn decreased with time. The processes associated with the decrease in extractability in DTPA of Zn added to soil can be described aptly by a diffusion equation which gives the proportion of added Zn in the non-DTPA fraction as a function of the square root of incubation time. This result suggests that the diffusion of Zn cations into microporous solids is a rate-limiting reaction. The relative diffusion rate coefficients (D/r²) were found to be 1.95×10^-10 and 3.34×10^-10 sec^-1 in the soils with added Zn of 20 and 60 mg kg^-1, respectively. Compared with uncropped soil, the concentrations of DTPA-Zn in the soils with added Zn were decreased by cropping. The decrease of DTPA-Zn in the soils in the presence of corn can be attributed to both its acquisition by corn and other processes associated with the growing of corn. The activity of plant roots would appear to enhance the process of decrease in the extractability in DTPA of Zn added to the soil. The source of Zn uptake by corn was affected by the loading or activity of Zn in soil. In the soil with low available Zn, the DTPA non-extractable Zn (non-DTPA-Zn) was mobilized and taken up by corn. In the soils with high available Zn, e.g. the recently added Zn, only EXC-Zn and a part of the DTPA-Zn were taken up by corn.     

北京鸭红细胞铜锌超氧化物歧化酶电荷异构体的分离和某些性质

等电聚焦表明,北京鸭红细胞铜锌超氧化物歧化酶由等电点分别为５．０,５．３,５．９,６．１和６．５的五个主要的活性组分（电荷异构体）构成,利用分析型聚丙烯酰胺凝胶等电聚焦电泳进行电荷异构体的制备级分离,采用三氯乙酸沉淀法快速确定蛋白条带的位置,电渗洗脱法回收蛋白,获得其中两个电荷异构体,对比研究结果表明电荷异构体的活性,氨基酸组成,二级结构等性质无明显差异。     

Mercury (Hg2+) and zinc (Zn2+): Two divalent cations with different actions on voltage-activated calcium channel currents

Summary 1. We examined the actions of mercury (Hg²⁺) and zinc (Zn²⁺) on voltage-activated calcium channel currents of cultured rat dorsal root ganglion (DRG) neurons, using the whole-cell patch clamp technique.2. Micromolar concentrations of both cations reduced voltage-activated calcium channel currents. Calcium channel currents elicited by voltage jumps from a holding potential of –80 to 0 mV (mainly L- and N-currents) were reduced by Hg²⁺ and Zn²⁺. The threshold concentration for Hg²⁺ effects was 0.1 µM and that for Zn²⁺ was 10µM. Voltage-activated calcium channel currents were abolished (>80%) with 5µM Hg²⁺ or 200µM Zn²⁺. The peak calcium current was reduced to 50% (IC₅₀) by 1.1µM Hg²⁺ or 69µM Zn²⁺. While Zn²⁺ was much more effective in reducing the T-type calcium channel current—activated by jumping from –80 to –35 mV—Hg²⁺ showed some increased effectiveness in reducing this current.3. The effects of both cations occurred rapidly and a steady state was reached within 1–3 min. While the action of Zn²⁺ was not dependent on an open channel state, Hg²⁺ effects depended partially on channel activation.4. While both metal cations reduced the calcium channel currents over the whole voltage range, some charge screening effects were detected with Hg²⁺ and with higher concentrations (>100µM) of Zn²⁺.5. As Zn²⁺ in the concentration range used had no influence on resting membrane currents, Hg²⁺ caused a clear inward current at concentrations µM.6. In the present study we discuss whether the actions of both metals on voltage-activated calcium channel currents are mediated through the same binding site and how they may be related to their neurotoxic effects.     

Effect of β-alanyl-L-histidinato zinc on differentiation of osteoblastic MC3T3-El cells: Increases in alkaline phosphatase activity and protein concentration

The effect of -alany-L-histidinato zinc (AHZ) on bone cell function was investigated in osteoblastic MC3T3-E1 cells. Cells were cultured for 3 days at 37°C in a CO₂ incubator in plastic dishes containing -modified minimum essential medium supplemented with 10% fetal bovine serum. After the cultures, the medium was exchanged for that containing 0.1% bovine serum albumin plus AHZ (10^–7–10^–5 M) or other reagents, and the cells were cultured further for appropriate periods of time. The presence of AHZ (10^–7–10^–5 M) produced a remarkable increase of alkaline phosphatase activity and protein concentration in osteoblastic cells. Thus increases were seen with the prolonged cultivation (12–21 days). With the culture of 1, 3 and 12 days, the effect of AHZ (10^–6 M) to increase alkaline phosphatase activity and protein concentration was more intensive than the effect of zinc sulfate, (10^–6 M). The AHZ effects were completely abolished by the presence of cycloheximide (10^–6 M), indicating that AHZ stimulates protein synthesis in the cells. The present study suggests that AHZ has a stimulatory effect on cell differentiation, and that this effect is partly involved on protein synthesis in osteoblastic cells.     

Poly(ADP-ribose) polymerase: Structural conservation among different classes of animals and its implications

Poly(ADP-ribose) polymerase cDNAs have been isolated from different classes of animals. Cloning of genes from lower eukaryotes has allowed us to investigate directly the biological functions of poly(ADP-ribosyl)ationin vivo. The conservation of specific regions among mammals, chicken,Xenopus laevis, andDrosophila melanogaster reveals the essential structural elements required for recognition of breaks in DNA and for catalytic activity. Cys, His and basic residues in the zinc-finger consensus region are conserved. The carboxyl terminal region corresponding to an NAD-binding domain is strongly conserved. The dinucleotide-binding consensus sequence and 1-A-2, Rossmann fold structure, and -sheet structures are completely conserved from mammals to insect. InDrosophila, a putative leucine-zipper motif has been identified, and other poly(ADP-ribose) polymerases also contain an -helical, amphipathic structure in the auto-modification domain. In this article, we review the recent structural analyses of the functional domains of poly(ADP-ribose) polymerase in phylogenetically divergent species, and discuss the implications of structural conservation for its biological functions.Abbreviations aa amino acid(s) - D. melanogaster Drosophila melanogaster - PARP poly(ADP-ribose) polymerase [EC 2.4.2.30] - PCR polymerase chain reaction - X. laevis Xenopus laevis     

Extrahepatic tissue copper concentrations in white perch with hepatic copper storage

Hepatic copper storage in man (Wilson's disease), Bedtington and West Highland white terriers, and white perch ( Morone americana ) is characterized by the progressive accumulation of copper in hepatic lysosomes bound to cytoprotective metallothionein. In man, saturation of the liver storage capacity results in the distribution of copper to extrahepatic tissues with multiple organ system dysfunction. To determine if extrahepatic tissue copper concentrations also increase in white perch, copper and zinc levels in liver, brain, heart, gills, serum, and bile were determined by atomic absorption spectrophotometry and compared to striped bass ( Morone saxatilis ). Results showed that brain copper concentrations in. white perch were elevated and significantly correlated with liver copper. Bile and serum copper also increased significantly with liver copper. Copper levels in heart and gill tissues were low. Liver zinc was increased in white perch but not to the same magnitude as copper, and was correlated significantly with liver copper; possibly a non-specific secondary increase related to an overall increase in hepatic metallothionein. Histochemical staining of liver with rubeimc acid for copper was proportional to copper concentrations, and clusters of positive mononuclear cells were also seen in brain and spleen. Foci of macrophages in spleen were also intensely positive with Perl's iron stain which may have been indicative of haemolysis. The patterns of copper distribution seen in white perch present a useful comparative model to study alterations in copper metabolism.     

Efficiency of serum copper/zinc ratio for differential diagnosis of patients with and without lung cancer

We examined serum copper (Cu), serum zinc (Zn), and the serum copper/zinc ratio (Cu/Zn) in 162 patients. All of them were seen to have an abnormal shadow in the chest X-ray films, that is, 109 patients with lung cancer (LC) and 53 patients with no lung cancer (NLC). The mean Cu and Cu/Zn in LC patients were significantly higher than those in NLC patients (p<0.05). In LC patients, Cu and Cu/Zn were higher and Zn was lower in advanced tumors than early ones. There was a significantly clear relation between Cu or Cu/Zn and the tumor (T) stages. When the relative risk (RR) of LC was estimated, it was seen that the higher Cu and Cu/Zn became, the higher RR became. Furthermore, we showed the sensitivity of the receiver operator characteristic of the test (ROC) curve for Cu, Cu/Zn, and carcinoembryonic antigen (CEA) to diagnose LC, as explained in a paragraph of methods.The determinations of Cu, Zn, and Cu/Zn are simple and inexpensive. They also appear to have a great diagnostic value in determining the local invasion of LC and as a screening test in the high-risk patients for LC.     

The binding of zinc,but not cadmium,by phytic acid in roots of crop plants

Plant species adapted to soils enriched with heavy metals often accumulate these metals in their above or below ground organs. In this study, electron probe microanalysis of fractured, quench-frozen root specimens of common crop species shows that an appreciable quantity of Zn can be bound as Zn phytate (myo-inositolkis-hexaphosphate) within small vacuoles of cells in the root elongation zone of lucerne, soybean, lupins, tomato, rapeseed, cabbage, radish, maize and wheat exposed to high levels of Zn (80–300 M). Globular deposits of Zn phytate are most frequently observed in the endodermis of dicotyledonous species and in the pericycle of monocotyledonous species, but may also occur in the stele and inner cortex after prolonged exposure to toxic levels of Zn. The deposits could not be found in Zn-treated sunflower, field peas and Italian ryegrass. In three crop species, lucerne, soybean and maize, Zn-induced phytate globules were frequent, but exposure of roots to 30 M Cd did not induce the formation of Cd-containing globular deposits as observed inLemna minor (Van Steveninck et al., 1990a, 1992). Simultaneous Zn and Cd treatment induced the formation of Zn phytate globules as effectively as Zn alone, and Cd was not detected in the deposits.     

Effect of shock-loading of heavy metals on total organic carbon and phosphate removal in an anaerobic-aerobic activated sludge process

The effect of shock-loading of zinc, copper and cadmium ions on the removal of total organic carbon (TOC) and phosphate in an anaerobic-aerobic activated sludge process was investigated. TOC removal was not sensitive to shock-loading of Zn²⁺ and Cd²⁺ ions, and complete removal was achieved even at 20 mg Zn²⁺/l and 20 mg Cd²⁺/l. However, with over 1 mg Cu²⁺/1 TOC removal efficiency decreased. PO _inf4 ^sup3- removal, in contrast, was extremely sensitive to these metal ions, with the threshold being 1 mg Zn²⁺/l and 1 mg Cd²⁺/l. Higher concentrations adversely affected PO _inf4 ^sup3- removal. Copper again proved detrimental; no PO _inf4 ^sup3- removal was achieved even at 1 mg Cu/l. These results highlight the sensitivity of the removal efficiencies of TOC and PO _inf4 ^sup3- to shock loadings of these heavy metals.Y.P. Ting is with the Department of Chemical Engineering, National University of Singapore, Kent Ridge, 0511, Singapore; H. Imai and S. Kinoshita are with the Department of Chemical Process Engineering, Hokkaido University, Sapporo 060, Japan.     

A 70-amino acid zinc-binding polypeptide fragment from the regulatory chain of aspartate transcarbamoylase causes marked changes in the kinetic mechanism of the catalytic trimer.

Interaction between a 70-amino acid and zinc-binding polypeptide from the regulatory chain and the catalytic (C) trimer of aspartate transcarbamoylase (ATCase) leads to dramatic changes in enzyme activity and affinity for active site ligands. The hypothesis that the complex between a C trimer and 3 polypeptide fragments (zinc domain) is an analog of R state ATCase has been examined by steady-state kinetics, heavy-atom isotope effects, and isotope trapping experiments. Inhibition by the bisubstrate ligand, N-(phosphonacetyl)-L-aspartate (PALA), or the substrate analog, succinate, at varying concentrations of substrates, aspartate, or carbamoyl phosphate indicated a compulsory ordered kinetic mechanism with carbamoyl phosphate binding prior to aspartate. In contrast, inhibition studies on C trimer were consistent with a preferred order mechanism. Similarly, 13C kinetic isotope effects in carbamoyl phosphate at infinite aspartate indicated a partially random kinetic mechanism for C trimer, whereas results for the complex of C trimer and zinc domain were consistent with a compulsory ordered mechanism of substrate binding. The dependence of isotope effect on aspartate concentration observed for the Zn domain-C trimer complex was similar to that obtained earlier for intact ATCase. Isotope trapping experiments showed that the compulsory ordered mechanism for the complex was attributable to increased "stickiness" of carbamoyl phosphate to the Zn domain-C trimer complex as compared to C trimer alone. The rate of dissociation of carbamoyl phosphate from the Zn domain-C trimer complex was about 10(-2) that from C trimer.(ABSTRACT TRUNCATED AT 250 WORDS)