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Biomedical subjects

U Weser

Publications and source records attributed to U Weser.

At least 91 records · Page 5Linked to original sources
PubMed1979

Models for metal-sulfur coordination in copper proteins.

The oxidation state of copper in several model compounds containing copper coordinated to sulfur, some of which are suggested model compounds for naturally occurring Cu-S chromophores, was determined employing x-ray photoelectron spectrometry. Copper was found to be present in a 3d10 state, which is characteristic for Cu(I). An initial photoreduction is excluded, as Cu(ethylenediamine)2 (SCN)2, in which a Cu-S bond is also present, was found to contain Cu(II) (3d9). As was the case with native parsley plastocyanin, the model compounds reacted effectively with superoxide anion radicals. We suggest that the electrons of the metal-sulfur chromophore in blue copper proteins are delocalized and that an equilibrium: RS--Cu(II) in equilibrium or formed from RS.Cu(I) exists.

Copper↗
PubMed1978

Partial purification, characterization and translation in vitro of rat liver metallothionein messenger ribonucleic acid.

Poly(A)+ (polyadenylated) mRNA coding for metallothioneins was purified 13-fold from rat liver polyribosomes and was identified by its ability to direct the biosynthesis of these proteins in a wheat-germ cell-free system. The carboxymethylated products of the protein-synthesizing system in vitro were analysed with sodium dodecyl sulphate/20% polyacrylamide-gel electrophoresis. The labelled compounds [3H]serine and [35S]cysteine were incorporated at high specific radioactivity into proteins that co-migrated with authentic metallothioneins. No [3H]leucine incorporation was found, in agreement with the amino acid composition of the metallothioneins. Metallothionein mRNA had a sedimentation coefficient of 9 S and carried a maximum of four ribosomes. At 5 h after a subcutaneous injection of ZnCl2 or CdCl2 (10 mumol/kg body wt.), the amount of this mRNA increased approx. 2- and 4-fold respectively, on the basis of translation in vitro. The increase in metallothionein mRNA (defined by translation in the wheat-germ system) was transient and, after CdCl2 treatment, fell back to control values by 17 h. Metallothioneins constituted a maximum of 0.8% of the total protein products synthesized in the wheat-germ system by total mRNA isolated from rat liver after CdCl2 treatment.

Animals↗
PubMed1978

Involvement of superoxide in the catalytic cycle of diamine oxidase.

The reaction of pig kidney diamine oxidase (amine:oxygen oxidoreductase (deaminating) (pyridoxal-containing), EC 1.4.3.6) could be significantly inhibited by superoxide dismutase active copper chelates but not by native 2Cu,2Zn-superoxide dimutase (cuprein). The ligands alone as well as Cd2+, a heavy metal of similar toxicity to Cu2+, showed no inhibition whatsoever. This indicates that .O-2 participates in the catalytic cycle and is produced at a site scarcely accessible to such a large molecule as cuprein. A mechanism for the second, aerobic step of the diamine oxidase reaction is suggested.

Amine Oxidase (Copper-Containing)↗
PubMed1978

Circular dichroism of metallothioneins. A structural approach.

A comprehensive study on circular dichroism of metallothioneins containing Zn, Cd and Cu was carried out. The contributions of the metals, the sulphur and the polypeptide chain to the observed Cotton effects was shown. From the pH dependency of the extrinsic Cotton effects which are due to the metal-thiolate chromophore the stability of the metal clusters was found to decrease in the order Cu greater than Cd greater than Zn. The pH values corresponding to the dissociation of half of the bound metal ions are 0.44 for Cu-thionein, 3.05 for Cd-thionein and 4.6 for Zn-thionein. The extrinsic Cotton effects of Cd, Zn-thioneins of varying Cd to Zn ratio could be simulated using the difference circular dichroic spectra of Cd-thionein (bands at 227, 242.5 and 262 nm), Zn-thionein (bands at 225 and 244 nm) and the circular dichroic spectrum of cysteine-thionein (band at 200 nm, shoulder at 225 nm). Since during the dissociation of the metals the circular dichroic spectra exhibited changes only in amplitude and not in shape we can conclude that the dissociation of the metal ions involves the complete sequential degradation of metal clusters. In the near-ultraviolet region the metal-free proteins show only Cotton effects attributable to a disulphide chromophore. Thus Cotton bands are observed for cystine-thionein at 282.5 and 260 nm. From the intrinsic circular dichroism of Cd- and Zn-thionein (negative Cotton effect at 200 nm, shoulder at 225 nm) it follows that the protein conformation consists of less than 5% helical or pleated sheet structure and therefore has to be classified as unordered structure or "fixed" random coil

Cadmium↗
PubMed1978

Reactivity of antiinflammatory and superoxide dismutase active Cu(II)-salicylates.

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-[alpha]-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.

Animals↗
PubMed1977

Hepatic microsomal dealkylations. Inhibition by a tyrosine-copper (II) complex provided with superoxide dismutase activity.

The effect of a divalent copper-tyrosine complex has been evaluated in rat liver microsome-catalyzed dealkylations. The copper complex, which is provided with superoxide dismutase activity, inhibits at micromolar concentrations aminopyrine, p-nitroanisol, and 7-ethoxycoumarin dealkylations. It has also been found that cumene hydroperoxide-supported p-nitroanisol demethylation, the formation of a 440 nm species, and the formation of superoxide radicals are inhibited by the divalent copper complex. On the other hand, 3-chloroperbenzoic acid has been found to support a copper complex-insensitive 7-ethoxycoumarin dealkylation. Oxygen uptake by rat liver microsomes is also inhibited by the copper complex. The data support the concept that the copper complex acts as a superoxide dismutase at the level of a cytochrome P-450 intermediate species, liganded with superoxide anions.

Aminopyrine N-Demethylase↗
PubMed1977

Copper-thionein from fetal bovine liver.

It was of interest to examine whether or not a low molecular weight copper-rich metal-thionein was present in biological species which received no metal pretreatment at all. From bovine fetal liver an 8 Cu 2 Zn-thionein having a molecular weight of 11 500 was successfully isolated. 16% of the total copper present in the whole liver were recovered in this protein. During the isolation process anaerobic conditions had to be maintained to avoid uncontrolled oxidation leading to polymeric species and the loss of most of the copper. The similarity of both the present copper-thionein and the polymeric neonatal type mitochondrocuprein was shown. A comparison of different copper-thioneins containing variable amounts of copper was possible when xiCu from 280 nm to longer wavelength was determined. With respect to the ultraviolet properties there were no detectable differences between copper-thioneins prepared either in vivo or in vitro and the fetal copper-thionein. Furthermore, the positions of the Cotton effects as deduced from circular dichroism measurements were rather similar although the magnitude of the observed Cotton extrema was less pronounced and sometimes the signs were reversed. X-ray photoelectron spectrometric studies revealed a Cu(2p3/2) binding energy value of 932.9 eV. Unlike the S(2p1/2,3/2) value near 162 eV using Cu-thioneins from chicken liver or yeast the higher S(20p1/2,3/2) binding energy of 163.0 eV employing fetal Cu-thionein was attributed to partial oxidation of the protein moiety and/or a particular chemical environment. The second S(2p1/2,3/2) peak was assigned to the copper catalyzed oxidation of sulphur via OH to yield RSO-3. In the X-ray photoelectron spectrum of the apoprotein one homogeneous S(2p1/2,3/2) band at 163.7 eV was seen attributable to RSSR.

Amino Acids↗
PubMed1977

X-ray photoelectron spectrometry of copper-thiouracil complexes.

X-ray photoelectron spectrometry was applied to evaluate the correct oxidation number of copper in complexes with 2-thiouracil, 6-amino-2-thiouracil and 6-methyl-2-thiouracil. Regardless of the mode of preparation exclusively Cu(I) was bound to the different thiouracil compounds, producing one homogeneous signal of the Cu2p3/2 electrons at 932.5 eV. Upon oxidation with H2O2, a typical Cu(II) satellite appeared in the main signal of the Cu2p3/2 level was shifted to higher binding energy values. The reaction of Cu(II) with thioracil yielded identical complexes as above, in which Cu had the formal oxidation state +I. During this reaction portions of the thiouracil were oxidized to 2,2'-dithiobis(4-pyrimidinol) [bis(4-hydroxy-2-pyrimidinyl)disulphide], as seen by the shifted sulphur 2p signals to 163.5 eV. After treating the Cu-thiouracil complexes with H2O2, the simultaneous presence of sulphur species having the oxidation states RStheta (161 eV), RSSR (163.5 eV) and RSOtheta3 (168.5 eV) is indicated by the ESCA signals monitored.

Copper↗
PubMed1977

Conformational changes induced by ionic strength and pH in two bovine myelin basic proteins.

The structures of two biologically different myelin proteins, A1 from the central nervous system and P2 from the peripheral nervous system, were investigated. Both proteins were isolated from nerve tissues. Conformational changes in the homogeneous proteins were examined in aqueous solutions by means of circular dichroism measurements. The secondary structures of both proteins proved to be very stable between pH 2.5 and pH 11.7. Unlike the P2 protein, the A1 protein is stable up to pH 13 without detectable conformational changes. The stereochemistry of the polypeptide chains of both proteins is markedly different in the presence of urea. While the value of theta222 for the A1 protein changes linearly with increasing urea concentration, a sigmoidal curve was obtained for the P2 protein. The observed differences in the dichroic properties of the basic myelin proteins A1 and P2 indicate the possibility of further structure - function correlations.

Animals↗
PubMed1976

Copper(I) and copper(II) in complexes of biochemical significance studied by X-ray photoelectron spectroscopy.

X-ray photoelectron spectroscopic measurements of copper complexes of biochemical significance were carried out to permit the conclusion whether or not copper is present in the Cu(I) or Cu(II) state. Only one single homogeneous signal in the X-ray photoelectron spectra of the Cu(I) 2p1/2 and 2p3/2 levels was seen regardless whatever Cu(I) complex was used. By contrast one more or less split satellite in addition to the main 2p copper signal appeared when Cu(II) complexes were studied. The extent of satellite splitting was dependent on the nature of the ligands coordinated with Cu(II). Thus, a strong splitting was observed in the spectra of Cu-(trifluoroacetylacetonate)2 and Cu-(biuret)2Cl2 were Cu(II) is exclusively bound to oxygen having a formal double bond. No such splitting was seen in Cu(II) chelates where the metal was bound to single bonded oxygen and/or nitrogen. It excited great interest to see that in the antiferromagnetically coupled Cu(II) complexes Cu2-(succinate)2-4H2O, Cu-(HCCO)2, CuO and in the completely diamagnetic Cu2-(u,3-diphenyltriazene)4 complex Cu(II) could be detected. The reaction of Cu(I) and Cu(II) with the thiol sulphur of either cysteine, penicillamine or alpha-mercaptopropionylglycine yielded Cu(I) complexes. During the X-ray exposure of the different samples photoreduction of Cu(II) was not observed. For example, the satellite structure of the copper 2p levels using Cu(II)-cystine remained unchanged during the measurement.

Amino Acids↗
PubMed1976

Copper deficiency and erythrocuprein (2Cu, 2Zn-superoxide dismutase).

The activities of 2Cu,2Zn-superoxide dismutase, ferroxidase (ceruloplasmin), catalase and glutathione peroxidase were measured in the blood of rats during copper depletion. Two control groups of animals were used; one received the regular diet containing all essential components including copper and the other group was maintained on a diet, containing 1% the amount of copper in normal diet, copper being supplied as Cu(Leu)2 in the drinking water. Both groups showed no detectable differences, either in the copper content of blood or in the measured four enzymic activities. Excessive copper (injected intraperitoneally) caused only an insignificant rise in the enzymic activities (0-10%) compared to either control. After starting copper depletion ferroxidase activity decreases to 15% on the 15th day, while the 2Cu,2Zn-superoxide dismutase activity decreases to 40% on the 45th day. Ferroxidase activity shows rapid but transient changes immediately after perturbation in plasma copper levels. By contrast, the 2Cu,2Zn-superoxide dismutase activity more closely parallels the overall copper deficiency. Dietary repletion with copper raises the 2Cu,2Zn-superoxide dismutase activity to 94% and the ferroxidase activity to 80% of the control values within 36 h. Apart from the copper-dependent anemia catalase activity was decreased. However, 15 days after the start of the copper depletion catalase activity rises again and reaches the control value on the 40th day and a 30% stimulation was even seen on the 58th day. Upon copper repletion catalase activity reaches 166% of the control within 14 days. No copper-dependent differences of glutathione peroxidase activity were seen regardless whatever copper level was present in the rats.

Animals↗