Tissue-specific cadmium accumulation and metallothionein-like protein levels during acclimation process in the Chinese crab Eriocheir sinensis

Aquatic organisms chronically exposed to cadmium can increase their resistance to a subsequent elevated exposure. In order to investigate mechanisms involved in acclimation process in the Chinese crab Eriocheir sinensis, we compared Cd level as well as metallothionein-like protein (MTLP) content in different tissues after direct acute exposure (i.e. 500 microg Cd L(-1) for 3 days), and after acute following chronic (i.e. 10 or 50 microg Cd L(-1) for 30 days) exposure. Cadmium accumulation occurred in the following order: anterior gill>hepatopancreas>posterior gill>carapace>hemolymph>muscle. As high concentrations as 188 microg Cd g(-1) w.w. were reported in anterior gills and seem to reach a saturation level. In these gills, the highest MTLP induction was observed after a direct acute exposure, for which a correlation with Cd content occurred. However, the Cd-binding potential by MTLPs was exceeded for any exposure condition. In hepatopancreas, the highest Cd level was reported for crabs acclimated during 30 days to 50 microg Cd L(-1) before challenging with an acute exposure. Moreover, we showed that MTLPs were induced during the acclimation process. In this organ, MTLPs are theoretically sufficient to bind all Cd. These results suggest that during a chronic exposure to 50 microg Cd L(-1), Chinese crabs acquire the capacity to hold more cadmium in hepatopancreas where it can be sequestrated by MTLPs. On the contrary, MTLP induction seems to be a rapid response to acute exposure in anterior gill, but is not sufficient to sequester all Cd. Other sequestration and/or detoxification mechanisms must take place in anterior gill to cope with high Cd levels.     

The improvement of sensitivity in lead and cadmium determinations using flame atomic absorption spectrometry

Various designs of quartz tubes of the slotted tube atom trap were examined to improve the sensitivity of flame atomic absorption spectrophotometry. The studied designs include the diameter length and the length of the upper slot of quartz tubes. Tubes having a diameter of 5 and 6 mm and an upper slot length of 2.3 cm produce the best sensitivity—as high as 6- and 10-fold enhancement for lead (Pb) and cadmium (Cd), respectively. The limits of quantitation were found to be 35 and 4 ng ml⁻¹ for Pb and Cd, respectively, by the optimized method. The achieved technique was applied to determine the concentrations of Pb and Cd in cancerous (malign) and noncancerous (adenoma) human thyroid tissues.     

Synthesis and structural characterization of cadmium(II) complexes with 2-(2-pyridyl)imino-N-(2-thiazolin-2-yl)thiazolidine (PyTT)

We have carried out the synthesis of the cadmium coordination compounds [Cd(NO₃)₂(PyTT)(H₂O)] (1) and [CdCl₂{(μ-Cl)₂CdCl(μ-Cl)(μ-PyTT)Cd}₂]_n (2), together with their structural determination by means of X-ray diffraction. The compounds were also characterized through elemental analysis and infrared spectroscopy. The first complex presents a distorted pentagonal bipyramidal geometry with the axial positions occupied by one oxygen atom from a water molecule and a second one from a nitrate ion which acts as a monodentate ligand, whereas the equatorial plane contains three nitrogen atoms from the organic moiety and two oxygen atoms coming from the other nitrate group, which is bidentate. The structure of the second complex consists of parallel sheets linked by van der Waals forces, each one made up of structural units [CdCl₂{(μ-Cl)₂CdCl(μ-Cl)(μ-PyTT)Cd}₂], which possesses two PyTT ligands, 10 bridging chloro ligands and 5 cadmium(II) centres belonging to three environment types: octahedral CdN₂Cl₄, octahedral CdCl₆, on which a centre of symmetry is located, and tetrahedral CdNCl₃, present in a 2:1:2 ratio.     

Detection of a hidden folding intermediate in the focal adhesion target domain: Implications for its function and folding

The focal adhesion target (FAT) domain of focal adhesion kinase has a four-helix bundle structure. Based on a hydrogen exchange-constrained computer simulation study and some indirect experimental results, it has been suggested that a partially unfolded state of the FAT domain with the N-terminal helix unfolded plays an important role in its biological function. Here, using a native-state hydrogen exchange method, we directly detected an intermediate with the N-terminal helix unfolded in a mutant (Y925E) of the FAT domain. In addition, kinetic folding studies on the FAT domain suggest that this intermediate exists on the native side of the rate-limiting transition state for folding. These results provide more direct evidence of the existence of the proposed intermediate and help to understand the folding mechanism of small single domain proteins.     

Cadmium-Induced Inhibition of Apoplastic Ascorbate Oxidase in Barley Roots

The effect of excess cadmium (Cd: 0.0, 0.25, 0.5, 1.0 and 2.0 mM) on growth and ascorbate oxidase (AO) activity was investigated in barley (Hordeum vulgare L. cv. Jubilant) roots. The study employed a filter-paper technique to germinate and grow the germinating seeds following imbibition with respective Cd treatments for 4 h at 25 °C in darkness. Cd was required at 1.0 mM to affect 50% root growth inhibition 72 h after the treatment. This Cd-induced root growth inhibition was accompanied by a corresponding loss of plasma membrane integrity in root cells as evaluated by Evans blue uptake. Excess Cd (1.0 and 2.0 mM) significantly inhibited the AO activity in all the analysed fractions of barley roots such as extracellular, soluble, cell wall (CW)- and membrane-bound fractions. AO was localized in the apoplast, and its highest specific activity was detected in the CW II fraction obtained by extraction with 1.0 M NaCl from purified cell walls. The analysis of AO isozyme profile showed that besides the reduced activity of two anionic and two cationic isozymes, one cationic AO isozyme was activated during excess Cd treatment, which could be detected in cell wall fractions CW II, III and IV.     

Potential of cadmium sulphide nanorods as an optical microscopic probe to the folding state of cytochrome C

The folding behavior of cytochrome C (Cyt-C) conjugated with CdS nanorods (CdSnr) is amenable to monitoring by bright field microscopy, the porosity and percolating behavior of such protein conjugated nanoclusters depending on the folding history prior to the conjugation. The method has been used to predict the thermal melting behavior as well as guanidine hydrochloride induced unfolding of Cyt-C. Dynamic light scattering studies indicate that the size distribution of the nanoforms widens in presence of the protein. Furthermore, there is emergence of clusters with higher conductivity and altered zeta potential. Increase of second virial coefficient of CdS nanoforms in the presence of Cyt-C (obtained from static light scattering experiments) implies presence of protein coat over the hydrophobic nanosurface. The results are supported by morphological changes observed through scanning electron microscopy (SEM). Accordingly, the X-ray diffraction pattern shows a change of crystallographic orientations of CdSnr in presence of Cyt-C.     

Supramolecular architectures of cadmium(II) built of 2,2′-biimmidazole and bifunctional carboxylates: Syntheses, crystal structure and properties

A series of four new supramolecular complexes of cadmium(II), {[CdBr(H₂biim)(PyCO₂)(H₂O)](H₂O)}_∞ (1) (H₂biim = 2,2′-biimidazole, PyCO₂ = isonicotinate), [Cd(H₂biim)₂(HBDC)₂] (2) (H₂BDC = terephthalic acid), [Cd(H₂biim)₂(H₂O)₂](BDC) (3) and [Cd(H₂biim)₂(H₂O)₂](PyCO₂)₂ · 4H₂O (4) have been prepared and characterized by X-ray crystallography, IR, fluorescence spectra and thermogravimetric analysis. Compound 1 exhibits an infinite chain-like structure through bridging isonicotinate. Strong interchain hydrogen bonds between isonicotinate and H₂biim result in the robust 2-D sheet structure, responsible for the insolubility. The similar hydrogen bonds between H₂biim and the coordinated 1,4-bdc and complementary hydrogen bonds between monoprotonated bdc are responsible for the robust 2-D layered structure of 2 that is insoluble in aqueous solution. 1,4-Bdc becomes uncoordinated in the soluble complex 3, although it has hydrogen bonded 2-D structure as well.     

Crucial role of position 40 for interactions of CCK-58 revealed by sequence of cat CCK-58

Evidence suggests that amino terminal extensions of CCK-8 affect the carboxyl terminal bioactive region of CCK. Cat CCK-58 was purified by low pressure reverse phase and ion-exchange chromatography steps and several reverse phase HPLC steps. The purified peptide and its tryptic fragments were characterized by mass spectral analysis and microsequence analysis. The structure of cat CCK-58 is: AVQKVDGEPRAHLGALLARYIQQARKAPSGRMSVIKNLQSLDPSHRISDRDY(SO3) MGWMDF-amide. Cat and dog CCK-58 are identical except for position 40 which is serine in cat and asparagine in dog. Radioimmunoassay detected cat CCK-58 about 1/10th as well as dog CCK-58, indicating a marked effect on C-terminal immunoreactivity. Cat CCK-58 with a serine at position 40, the same residue found in pig, mouse, cow and rabbit CCK-58, can be used as a unique bioprobe for defining how amino terminal amino acids influence the structure and bioactivity of the carboxyl terminal region of CCK.     

Methyl chloride utilising bacteria are ubiquitous in the natural environment

A 17-kDa protein (CadI) was induced by cadmium in Mycobacterium bovis and Mycobacterium tuberculosis. Comparison of the N-terminal sequence from M. bovis CadI with the annotated M. tuberculosis genome database identified Rv2641 as the encoding gene. Long and short promoter fragments from M. bovis cadI were fused to the lacZ reporter gene in pYUB76. Only the long fragment directed cadmium-inducible activity when electroporated into M. bovis. The cadI promoter has potential for both constitutive and inducible expression studies in M. bovis and M. tuberculosis.     

Silicon modifies root anatomy, and uptake and subcellular distribution of cadmium in young maize plants

Background and Aims

Silicon (Si) has been shown to ameliorate the negative influence of cadmium (Cd) on plant growth and development. However, the mechanism of this phenomenon is not fully understood. Here we describe the effect of Si on growth, and uptake and subcellular distribution of Cd in maize plants in relation to the development of root tissues.

Methods

Young maize plants (Zea mays) were cultivated for 10 d hydroponically with 5 or 50 µm Cd and/or 5 mm Si. Growth parameters and the concentrations of Cd and Si were determined in root and shoot by atomic absorption spectrometry or inductively coupled plasma mass spectroscopy. The development of apoplasmic barriers (Casparian bands and suberin lamellae) and vascular tissues in roots were analysed, and the influence of Si on apoplasmic and symplasmic distribution of ¹⁰⁹Cd applied at 34 nm was investigated between root and shoot.

Key Results

Si stimulated the growth of young maize plants exposed to Cd and influenced the development of Casparian bands and suberin lamellae as well as vascular tissues in root. Si did not affect the distribution of apoplasmic and symplasmic Cd in maize roots, but considerably decreased symplasmic and increased apoplasmic concentration of Cd in maize shoots.

Conclusions

Differences in Cd uptake of roots and shoots are probably related to the development of apoplasmic barriers and maturation of vascular tissues in roots. Alleviation of Cd toxicity by Si might be attributed to enhanced binding of Cd to the apoplasmic fraction in maize shoots.