Bioinorganic chemistry最新文献

The half-lives of liver and kidney metallothionein of rats fed diets containing either 2,000 ppm Zn or 100 ppm Cd were determined by a single injection of ¹⁴C-cystine. This protein was purified by Sephadex G-75 and DEAE cellulose column chromatography. Half-lives of liver metallothionein in rats fed the basal (18 ppm Zn), high Zn (2,000 ppm Zn), high Zn then basal, and high Cd (100 ppm) diet were, respectively, 3.4, 2.7 1.3, and 3.3 days, and that of kidney metallothionein were, respectively, 2.0, 2.2, 1.4, and 3.6 days. Thus, Cd-thionein has a longer half-life than Zn-thionein in both liver and kidney. The major species of metallothionein, which were separated on DEAE cellulose, had similar half-lives. Metallothionein, a protein having high content of metals and relatively short half-life, is possibly involved in cellular regulatory function.

Rate parameters are reported for the oxidation of cuprous stellacyanin by Co(PDTA)⁻ (k(25.0°) = 17.9 M⁻¹sec⁻¹, Δ H^≠ = 8.5 kcal/mol. ΔS^≠ = −24 cal/mol-deg; pH 7.0, μ 0.5 M) and Co(CyDTA)⁻ (k(25.1°) = 17.0 M⁻¹ sec⁻¹, ΔH^≠ = 8.7 kcal/mol, ΔS^≠ = −24 cal/mol-deg; pH 7.0, μ 0.5 M). The first order Co(PDTA)⁻ and Co(CyDTA)⁻ dependences observed over wide concentration ranges contrast with the saturation behavior reported previously for Co(EDTA)⁻ as the oxidant. It is concluded that the -CH₃ and -(CH₂)₄-substituents of PDTA and CyDTA, respectively, prevent the alkylated derivatives of Co(EDTA)⁻ from hydrogen bonding with the reduced blue protein, causing precursor complex formation constants to fall far below that of 149 M⁻¹ (25.1°) observed for the EDTA complex. The similarity between ΔH^≠ and ΔS^≠ values for the oxidation of stellacyanin by Co(PDTA)⁻ and Co(CyDTA)⁻ indicates that the size of alkyl substituents linked to the carbon atoms of the EDTA ethylenediamine backbone has little influence on activation requirements for Cu(I) to Co(III) electron transfer. The electron transfer reactivity of aminopolycar☐ylatocobalt(III) complexes with cuprous stellacyanin therefore appears to be linked to the accessibility of one or more of the ligated acetate groups to outer-sphere contact with the type 1 Cu(I) center. Saturation in k_obsd vs. [oxidant] plots found for the reactions of Co(PDTA)⁻ and Co(CyDTA)⁻ with stellacyanin at pH 6 and at pH 7 in the presence of EDTA is attributed to the formation of “dead-end” oxidant-protein complexes.

The incorporation of trivalent chromium into S. carlsbergensis as function of time, the effects of chromium and glucose concentrations in the medium on the uptake of⁵¹Cr by the yeast cells, and the effect of chromium on growth of the yeast were studied.

⁵¹Cr was taken up by yeast cells most rapidly during the logarithmic growth period in Sabouraud's liquid medium containing 5% glucose. Cells grown in a medium containing only 0.5% glucose at the beginning of cultivation incorporated very little⁵¹Cr, and incorporation ceased when the glucose concentration was reduced to less than 0.1%. Addition of 5% glucose into this culture resulted in a very rapid increase in the⁵¹Cr uptake. The second glucose addition did not notably increase the rate of⁵¹Cr uptake by the yeast. Chromium, reduced yeast growth slightly, however, was not clearly toxic.

A kinetic study of the oxidation of the copper(I) form of the blue copper protein stellacyanin (St(I)) by Co(EDTA)^- has been performed. Observed rate constants approach a saturation limit with increasing [Co(EDTA)^-] at pH 7, consistent with a mechanism involving rapid pre-equilibrium oxidant-protein complex formation followed by rate-limiting intramolecular Cu(I) to Co(III) electron transfer:

The activity of chelated Cu(II) with four different aspirin-like drugs in various superoxide dismutase assays was examined. Prior to these studies the oxidation state of the involved copper was measured by x-ray photoelectron spectrometry and was found to be +II throughout. All copper complexes were able to suppress the xanthine-xanthine oxidase mediated reduction of both cytochrome c and nitroblue tetrazolium as well as the formazan formation by KO₂ in a specific manner. The hydroxylation of benzo-[α]-pyrene as well as the demethylation of 7-ethoxycoumarin using induced hepatic rat microsomes could be successfully inhibited by the employed Cu(II) chelates. Cu(II)-acetylsalicylate was the most active copper complex. Our findings support the proposal that Cu(II) chelates are the active forms of aspirin-like antiinflammatory agents.

The deoxyribonucleic acid polymerase I (deoxynucleoside triphosphate: DNA deoxynucleotidyl transferase; E.C 2.7.7.7) of Escherichia coli is inhibited more than 99% by 50 μM N-methylisatin-β-thiosemicarbazone (M-IBT) + 50 μM CuSO₄. When added alone, 50 μM M-IBT enhanced activity, whereas 50 μM CuSO₄ alone inhibits the reaction by 40%. Inhibition is reversed by the competing chelating agent ethylenediamine tetraacetate. A related compound, 1-formylisoquinoline thiosemicarbazone, also inhibits enzyme activity in the presence of cupric ions.

Polymerase inhibition by M-IBT + CuSO₄ is relieved when increasing amounts of nucleic acid, but not increasing amounts of enzyme, are added. This suggests that the DNA template, not the polymerase, is the target of inhibition by M-IBT + CuSO₄.

The biological pertinence of nucleic acid as a target for the M-IBT + CuSO₄ complex is shown by the binding of Rous sarcoma virus (RSV) 70 S RNA to the complex formed within the intact virus particle. The importance of metal ions for this drug action is supported by the ability of ethylenediamine tetraacetate to reverse the binding.

The appearance of oscillations in the Krebs cycle with metabolites such as oxaloacetic and citric acids has been confirmed experimentally in model systems utilizing Mn²⁺ as the catalyst and KBrO₃/H₂SO₄ as the oxidant. Oscillations occur over a range of concentrations of substrate. The oscillation period also depends on the metabolite concentration. It has been found that malic acid and oxaloacetic acid constitute a coupled oscillator system. The experiments are discussed in relation to other metabolite cycles.

Evidence is presented for a chemical equilibrium of gold(I) among sulfhydryl binding sites in the cytoplasm of renal cortical cells of the rat. The gold distribution among protein and nonprotein species, examined by gel-permeation chromatography following in vivo administration of gold sodium thiomalate, gold sodium thioglucose, NaAuCl₄, and (C₂H₅)₃PAuCl, was similar in each case, although the cytoplasmic gold concentrations varied. The pattern of gold elution closely parallels that of the thiol groups in the supernatant. In vitro addition of gold sodium thiomalate to the supernatant fraction produced an identical distribution. Addition of cysteine to cytoplasm following in vivo administration of gold drastically decreased the protein-bound gold and increased the non-protein-bound gold. These data rule out the induced synthesis of a metallothionein-like gold-binding protein. Ultracentrifugation revealed gold to be present in the microsomal fraction as well as the supernatant.

Paramagnetic cluster ions of the type Cu(II)₆Cu(I)₈L₁₂Cl^z, where z is charge and L a derivative of 1-amino-2,2-dimethyl-2-mercaptoethane, have been shown to produce detectable ¹H-nmr absorptions. Linewidths are narrow enough to permit the use of high resolution instruments. Downfield shifting of all detectable resonances is indicative of S → Cu²⁺ charge transfer, which results in a positive spin density at sulfur. Exchange measurements with ⁶⁷Cu indicate relatively static structures.