Impact of chromium ions on nucleoside triphosphates and nucleic acids

Paramagnetic 19F NMR and Electrospray Ionization Mass Spectrometric Studies of Substituted Pyridine Complexes of Chromium(III): Models for Potential Use of 19F NMR to Probe Cr(III)-Nucleotide Interaction

The synthesis and characterization of chromium basic carboxylate complexes, [Cr₃(O₂CR)₆L₃]⁺, containing trifluoroacetate, 3-fluoropyridine, 3-trifluoromethylpyridine, and 4-trifluoromethylpyridine are described. The substituted pyridine ligands are used as models of DNA bases to determine whether ¹⁹F NMR would be a potentially useful probe of the binding of Cr³⁺ to DNA. The ¹⁹F NMR resonances of the coordinated ligands, while broadened by delocalization of unpaired electron density from the S=3/2 chromic centers, are readily discernable, and the contact shifts are of sufficient magnitude that the signals from coordinated and free ligands can easily be differentiated. Thus, ¹⁹F NMR appears to be a potentially useful probe of the binding of Cr³⁺ to DNA containing F-labeled bases. Additionally, electrospray MS is shown to be a convenient method to establish the identity of chromium basic carboxylate assemblies.

Cometabolism of Cr(VI) by Shewanella oneidensis MR-1 produces cell-associated reduced chromium and inhibits growth

Microbial reduction is a promising strategy for chromium remediation, but the effects of competing electron acceptors are still poorly understood. We investigated chromate (Cr(VI)) reduction in batch cultures of Shewanella oneidensis MR-1 under aerobic and denitrifying conditions and in the absence of an additional electron acceptor. Growth and Cr(VI) removal patterns suggested a cometabolic reduction; in the absence of nitrate or oxygen, MR-1 reduced Cr(VI), but without any increase in viable cell counts and rates gradually decreased when cells were respiked. Only a small fraction (1.6%) of the electrons from lactate were transferred to Cr(VI). The 48-h transformation capacity (Tc) was 0.78 mg (15 micromoles) Cr(VI) reduced. [mg protein](-1) for high levels of Cr(VI) added as a single spike. For low levels of Cr(VI) added sequentially, Tc increased to 3.33 mg (64 micromoles) Cr(VI) reduced. [mg protein](-1), indicating that it is limited by toxicity at higher concentrations. During denitrification and aerobic growth, MR-1 reduced Cr(VI), with much faster rates under denitrifying conditions. Cr(VI) had no effect on nitrate reduction at 6 microM, was strongly inhibitory at 45 microM, and stopped nitrate reduction above 200 microM. Cr(VI) had no effect on aerobic growth at 60 microM, but severely inhibited growth above 150 microM. A factor that likely plays a role in Cr(VI) toxicity is intracellular reduced chromium. Transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) of denitrifying cells exposed to Cr(VI) showed reduced chromium precipitates both extracellularly on the cell surface and, for the first time, as electron-dense round globules inside cells.

The binding of zinc(II) to Mung Bean Nuclease. A voltammetric study

Binding of zinc to Mung Bean Nuclease was investigated by anodic stripping voltammetry and cyclic voltammetry. These methods rely on the direct monitoring of the oxidation current of zinc in the absence and presence of Mung Bean Nuclease. Titration curves of Zn(2+) with the enzyme were obtained in concentrations ranging from 1.08x10(-9) to 1.07x10(-8) M and 1.16x10(-8) to 1.04x10(-7) M. The acquired data were used to calculate the dissociation constant and the stoichiometry of the complex. The binding sites of zinc in the Mung Bean Nuclease molecule were investigated using cyclic voltammetry. Two types of binding sites for zinc were identified and were attributed to a mononuclear exposed zinc-binding site with catalytic function and to an inaccessible binuclear zinc-binding site with structural functions.

Effects of chromium on health status, blood neutrophil phagocytosis and in vitro lymphocyte blastogenesis of dairy cows

The objective of this study was to determine the effects of supplemental dietary chromium (Cr) on health status and mastitis-related parameters, as well as neutrophil phagocytic activity of dairy cows during late pregnancy and early lactation. In addition, possible interactions and involvements of Cr with insulin, cortisol, somatotropin (rBST) and insulin-like growth factor-1 (IGF-1) were directly investigated in vitro based on blastogenic responses using peripheral blood lymphocytes (PBL) of eight cows fed the control diet. Forty pregnant Holsteins, 18 primiparous and 22 multiparous, at week (wk) 6 before the expected calving dates were randomly assigned to treatments: control and supplemental chelated Cr (0.5 ppm) in the diet. All cows were managed in a normal production operation and health status was assessed by recording the incidence of health problems during the experimental period of wks 6 before and 16 after calving (-6 to 16 wks). Mastitis-related parameters included somatic cell counts (SCC), bacterial colony counts of milk samples from each mammary gland quarter of all cows during wk 1 to wk 8 postpartum. Peripheral blood neutrophil phagocytic function of eight cows fed either control or supplemental Cr diet was determined by the ability to take up uniform fluorescent beads measured by flow cytometry. Supplemental Cr had no effect (P > 0.10) on health status of cows during late pregnancy and early lactation, or on SCC and bacterial colonies of quarter milk samples from early lactation (wks 1 to 8). Supplemental Cr also did not affect neutrophil phagocytic function of cows from 6 wks prepartum to 6 wks postpartum. However, in the in vitro study of PBL (from control animals, not fed Cr diet) blastogenesis with addition of insulin or cortisol at two levels (0.05 and 0.5 ng ml-1), insulin and cortisol enhanced or had no effect on PBL proliferations with or without concanavalin A (con A) simulation. However, further Cr addition in the culture medium containing supplemental insulin or cortisol, particularly CrCl3, additively increased (P < 0.05) BPL blastogenic activities with or without con a stimulation. Conversely, addition of rBST or IFG-1 (0.5 and 5.0 ng ml-1) in the culture medium enhanced PBL proliferation, but addition of Cr gave no additional effect. These results indicated that supplemental Cr had no beneficial effect on health status, mastitis-related parameters or neutrophil phagocytic activity of dairy cows. However, in vitro study confirmed and extended our previous observations that Cr has an effect on lymphocyte proliferation and this may associate with insulin or cortisol actions.

In vitro studies on the DNA impairments induced by Cr(III) complexes with cellular reductants

The influence of Cr(III) complexes with ascorbic acid, cysteine and glutathione on DNA has been studied spectrophotometrically and chromatographically. The toxic and genotoxic activities of these complexes were also investigated. It was found that these complexes bind to DNA weaker than hexaaqua Cr(III) complexes. It could be explained through the greater strength of the bi- and tridentate ligands coordinated to chromium in comparison to water molecules. The formation of DNA-DNA intermolecular bonds and DNA interstrand cross-linking has been also observed. These complexes were found to be non-toxic and non-genotoxic in the bacterial test.