Bioinorganic chemistry最新文献

Spectrophotometric studies have provided evidence for zinc-mediated ternary complexes between ATP and aromatic amino acids. The hypochromicity observed in the 260 nm band of ATP increased in the order phenylanine <tyrosine<tryptophan. Adding alanine did not produce any change of the ATP spectrum. The association constant was four fold higher for the ATP-Zinc-Tryptophan complex than for that of the ATP-Zinc-Alanine. The increased stability of the former complex was ascribed to the stacking interaction between indole and adenine rings. The maximum concentrations of the ATP-Zinc-Tryptophan complex occurred at about pH 8.0. For these ternary complexes several possible stacked structures involving or not involving N(7) of adenine are discussed.

This paper reports on ¹H and ³¹P NMR as well as EPR measurements of the labeling reagent of ATPase sites, “Co(III)-(phen)-ATP.” This complex is found to be paramagnetic, as deduced both from its EPR spectrum and from the significant broadening, though almost unshifted, proton and phosphorus resonances. This paramagnetism is a result of the incorporation of the superoxide free-radical anion in the coordination sphere of the trivalent cobalt ion. Evidence for the presence of superoxide in the complex is based on competition experiments with cyanide, which is able to displace the superoxide anion. The latter was identified by its inducing effect on the photoreactivity of luminol. The displacement of superoxide by cyanide was accompanied by the abolition of the paramagnetism of the complex. The relative distances between the protons and phosphorus atoms of ATP and the superoxide anion in the complex were calculated using the NMR line-broadening data. Structural models compatible with the experimental results are proposed. Under conditions of excess of adenine nucleotides or phenanthroline, the coordinated ATP molecule becomes exchangeable. This phenomenon is attributed to the labilization of the cobaltic ion ligands induced by the superoxide anion.

The possible structural basis of the specific inhibitory action of cuprein on the autoxidation of catecholamine was examined. The chiroptical properties of the native enzyme were compared with both the denatured and the apoprotein and the superoxide-dismutase-active Cu(Tyr)₂. Apart from the reduction of cuprein copper to Cu(I), marked and characteristic changes in the circular dichroism (CD) spectrum from 260–400 nm in the presence of adrenaline and oxygen were seen, suggesting the formation of a ternary complex. This conformational change proved dependent on the concentration of oxygen, adrenaline, and cuprein copper and was not seen when the apoprotein or the heat-denatured enzyme was used. Blocking of the vicinal hydroxyl groups of adrenaline by borate did not significantly affect the formation of the complex. This implies an essential role of the catecholamine side chain. It was assumed that the ligands in close proximity around the copper appear to be even more important for the catalytic action than the involved copper. No such specificity was measured when Cu(Tyr)₂ was used. Removal of the adrenaline side chain altered the enzymic function of added cuprein copper signifiantly. During the autoxidation of 1,2-dihydroxybenzene, cuprein copper accelerated the oxidation, whereas Cu(Tyr)₂ was essentially inactive.

The facultative potentially tetradentate thioether ligands 1,2-bis(2-methylthioethylthio)ethane (2,2,2), 1,3-bis(2-methylthioethylthio)propane (2,3,2) and 1,2-bis(3-methylthiopropylthio)ethane (3,2,3) react with copper(II) salts to form Cu₂(2,2,2)Cl₄, Cu₃(ligand)X₆ (ligand = 2,3,2 and 3,2,3 X = Cl; ligand = 2,2,2 2,3,2 and 3,2,3 X = Br), and Cu(ligand)(ClO₄)₂. The stoichiom-

The electronic properties of 2:1 sulfhydryl- and imidazole-containing peptide-Co(II) complexes have been investigated and compared with those of Co(II)-substituted “blue” copper proteins. The Co(II) complexes of N-mercaptoacetyl-L-histidine and 3-mercaptopropionyl-L-histidine gave the ligand field parameters of Δ_t = 4110 and B = 756 cm^-1, and of Δ_t = 4120 and B = 724 cm^-1, respectively. These values correspond well to those (Δ_t = 4900 and B = 730 cm^-1) of Co(II)-substituted “blue” copper proteins. The energy differences between S → M(II) charge transfer bands of Co(II)-Cu(II) couples were about 14,000 cm^-1 in both the proteins and the model complexes. The spectral results suggest that “blue” copper site has a pseudotetrahedral geometry and a deep absorption near 600 nm attributes to S → Cu(II) charge transfer.

The affinity of bicarboxylate ions (from oxalate to glutarate) for cobalt(II) bovine carbonic anhydrase has been investigated and compared with that of acetate and propionate. The oxalate ion shows a much greater affinity for the enzyme than acetate, whereas the other bicarboxylate ions have very little tendency to bind the enzyme. In every case, and particularly for the oxalate, the apparent affinity constants dramatically increase with decreasing pH.

On the basis of the electronic spectra a five-coordinate structure is proposed for all of the above derivatives. Carbon-13 NMR data have been discussed in terms of the oxalate ion chelating the metal ion and/or interacting with the wall of the active cavity.

Inactivation of chicken liver xanthine dehydrogenase by arsenite is reflected in the molybdenum electron paramagnetic resonance signal at g = 1.97. The arsenite spectrum shows additional splittings and considerable broadening yet remains comparable to the native in total intensity. Further subtle alterations of the molybdenum signal of arsenite-treated enzyme are seen in the presence of purine-type substrates or inhibitors.

Complex formation and redox reactions between copper(II) ion and d-penicillamine were studied in detail as functions of the metal/-ligand ratio and the concentration of halide ions. It was established that a copper (I)-d-penicillamine polymeric complex of amphoteric character is formed when excess d-penicillamine is present. When the d-penicillamine/copper(II) ratio = 1.45 in the starting reaction mixture, a mixed valence complex with an intense red-violet color is formed. The formation of this compound, which contains 44% copper(II) ion, is greatly influenced by the experimental conditions, primarily by the concentration of halide ions. The main chemical and physical characteristics of the mixed valence complex were determined via magnetic and spectroscopic measurements. It was further established that a very intense blue complex is formed when the d-penicillamine/copper(II) ratio = 2 and halide ions are present. On the basis of the nature of the products formed under various conditions it was concluded that the copper(II)-d-penicillamine system may serve as a good model for studying the binding sites of copper-containing proteins.

Coenzyme M (2-mercaptoethanesulfonate, HSCH₂CH₂SO₃^—) reacts with methylcobalamin nonenzymatically in the pH-range between 6 and 14 to yield the S-methyl derivative (CH₃SCH₂CH₂SO₃^—). In addition, and also at lower pH, methane is produced by reductive cleavage of the CoC bond. With methylcobaloximes as the methyl group donors, methane production predominates, with insignificant S-methylation. The initial rates of methane production from methylcobaloximes with coenzyme M as the reductant correlate with the rates of methane production from these substrates with active cell extracts of Methanobacterium M.o.H.

Tetracycline forms chelate complexes with cupric, nickelous, and cobaltous ions that bind DNA when analyzed in a filter-retention assay. Tetracycline complexes with other metal ions including zinc, ferrous, ferric, manganous, magnesium, and calcium ions do not produce this effect. The tetracycline·copper complex binds the homopolymers polyriboadenylate, polyribouridylate, polyriboinosinate, and polyribocytidylate. The binding of polyribocytidylate is least effective. The preaddition of calcium ions interferes with the ability of tetracycline to form a DNA-binding complex with cupric ions. Calcium ions do not block DNA binding by an already formed tetracycline·copper complex.

Riboflavin interferes with the DNA-binding action of tetracycline in the filter-retention assay. This suggests a rationale for its reported antagonism of bacterial growth inhibition by tetracycline. Riboflavin does not block the DNA-binding activity of an already formed tetracycline·copper complex. None of the riboflavin·metal ion complexes tested are capable of binding DNA in the filter-retention assay.