Zur biologischen Bedeutung von Fe3+ und Cu2+ als Komplexbildner

Summary The possible role of the metabolism of heavy metal ions in the process of ageing is discussed. It is suggested that, during this process, Cu²⁺ and Fe³⁺ as strong complexing ions, inhibit the activity of other metal enzymes by replacing their metal ion-activator. The relative stability of Cu²⁺- and Fe³⁺-complexes with various chelating compounds related to biological systems has been determined.     

Ambivalent effect of protein binding on computed distributions of metal ions complexed by ligands in blood plasma.

Although the absolute concentrations of metal complexes in blood plasma are controlled by protein binding, the percentage distribution of transition metal ions amongst low molecular weight ligands is not. Thus, computer simulations which omit protein equilibria can nevertheless afford reliable information about such metals in the biofluid.     

Investigating metal-binding in proteins by nuclear magnetic resonance

Metal ions play a key role for the function of many proteins. The interaction of the metal ion with the protein and its involvement in the function of the protein vary widely. In some proteins, the metal ion is bound tightly to the ligand residues and may be the key player in the function of the protein, as in the case of blue copper proteins. In other proteins, the metal ion is bound only temporarily and loosely to the protein, as in the case of some metalloenzymes and other proteins where the metal ion acts as a cofactor necessary for the function of the protein. Such proteins are often known as metal ion-activated proteins. The review focuses on recent nuclear magnetic resonance (NMR) studies of a series of metal-dependent proteins and the characterization of the metal-binding sites. In particular, we focus on NMR techniques for studying metal binding to proteins such as chemical shift mapping, paramagnetic NMR and changes in backbone dynamics upon metal binding. Received 12 October 2006; received after revision 30 November 2006; accepted 5 February 2007     

The CorA family: Structure and function revisited

The CorA family is a group of ion transporters that mediate transport of divalent metal ions across biological membranes. Metal ions are essential elements in most cellular processes and hence the concentrations of ions in cells and organelles must be kept at appropriate levels. Impairment of these systems is implied in a number of pathological conditions. CorA proteins are abundant among the prokaryotic organisms but homologues are present in both human and yeast. The activity of CorA proteins has generally been associated with the transport of magnesium ions but the members of the CorA family can also transport other ions such as cobalt and nickel. The structure of the CorA from Thermotoga maritima, which also was the first structure of a divalent cation transporter determined, has opened the possibilities for understanding the mechanisms behind the ion transport and also corrected a number of assumptions that have been made in the past.     

光致发光稀土有机配合物在生物分析上的应用

稀土有机配合物因镧系元素独特的电子结构而成为一类具有重要理论和应用价值的发光材料.本文综述了稀土有机配合物的类型及其光致发光的基本原理,阐述了稀土有机配合物光致发光在生物分析方面的应用,并在荧光免疫分析及活细胞成像方面提出了良好的展望.     

Zur Rolle von Schwermetallionen im Wirkungsmechanismus von Strahlenschädigung und Strahlenschutz

Summary The catalysis of the reaction between H₂O₂ and nucleotides by biologically important metal ions has been studied spectrophotometrically, the importance of complex-formation equilibria for this catalysis was demonstrated. Radiobiological implications are discussed.     

Metal binding to myosin and to myosin DTNB-light chain

Summary The effects of various divalent cations, Ca²⁺, Mg²⁺ and Mn²⁺ on the intrinsic fluorescence of heavy meromyosin (HMM) and myosin 5,5-dithio-bis-(2-nitrobenzoate) DTNB-light chain of rabbit striated muscle, are compared. At pH 6.4, the fluorescence change induced by the metal ions is present only in the isolated light chain and disappears in HMM, thus indicating an interaction between the heavy and light chains with respect to the binding of the metal ions. Whereas Mg²⁺ binds more strongly than Ca²⁺ to myosin, this order is reversed in the case of the DTNB-light chain.     

Strukturspezifischer oxydativer abbau von peptid-metall-komplexen

Summary The decapeptide polymxine B can be split into sub-units by hydrogen peroxide or by UV-irradiation when complexed with copper(II) or nickel(II); the splitting points are probably related to the points of attachment of the metal ions.     

Prokaryote-eukaryote interactions in trace element metabolism.Desulfovibrio sp. inHelix aspersa

Summary Snails (Helix aspersa) contain sulphate-reducing bacteria in their crops. Feeding such animals on food containing sulphate and molybdate ions does not induce a copper deficiency and in fact the bacteria appear to facilitate metal absorption. This is in contrast to the effects of these bacteria in ruminant cattle.     

Ambivalent effect of protein binding on computed distributions of metal ions complexed by ligands in blood plasma

Summary Although the absolute concentrations of metal complexes in blood plasma are controlled by protein binding, the percentage distribution of transition metal ions amongst low molecular weight ligands is not. Thus, computer simulations which omit protein equilibria can nevertheless afford reliable information about such metals in the biofluid.Acknowledgments. One of us (P. M. M.) thanks the University of Cape Town and the C. S. I. R. for financial assistance. Computations were performed on both of the University of Cape Town's UNIVAC 1106 system and the St. Andrews University's IBM 360/44. Address ofP. W. Linder: University of Cape Town, Rondebosch, Cape (South Africa).     

Zur Metallspezifität der Hexokinase

Summary The activity of hexokinase has been determined in the presence of different metal ions. Besides Mg²⁺, the ions Co²⁺, Ni²⁺, Mn²⁺, Zn²⁺, and Cd²⁺ show remarkable activation. The differences are explained by superposition of an activating and an inhibiting function. The specifity problem is discussed.     

Die katalytische Wirkung von Metallionen auf die Stabilität von Phosphagenen

Summary Phosphoroguanidates, a class of compounds which includes the enzymatically-active phosphagens, exhibit exceptionalin vitro stability. This lack of reactivity implies anin vivo mode of activation, as yet undiscerned. A variety of metal ions catalyse the cleavage of the phosphorus-nitrogen bond with consequent phosphoryl-group transfer, but the enhancement of rate seems insufficient to account for the known activities of phosphoro-creatine and phosphoro-arginine. It is suggested that yet another mode of activation, chemical or biochemical, awaits discovery.     

Deoxyribozymes: useful DNA catalysts in vitro and in vivo

Deoxyribozymes (DNA enzymes; DNAzymes) are catalytic DNA sequences. Using the technique of in vitro selection, individual deoxyribozymes have been identified that catalyze RNA cleavage, RNA ligation, and a growing range of other chemical reactions. DNA enzymes have been used in vitro for applications such as biochemical RNA manipulation and analytical assays for metal ions, small organic compounds, oligonucleotides, and proteins. Deoxyribozymes have also been utilized as in vivo therapeutic agents to destroy specific mRNA targets. Although many conceptual and practical challenges remain to be addressed, deoxyribozymes have substantial promise to contribute meaningfully for applications both in vitro and in vivo.     

Aquaporins with selectivity for unconventional permeants

The aquaporin protein family generally seems to be designed for the selective passage of water or glycerol. Charged molecules, metal ions and even protons are strictly excluded. Recently, particular aquaporin isoforms were reported to conduct unconventional permeants, i.e., the unpolar gases carbon dioxide and nitric oxide, the polar gas ammonia, the oxidative oxygen species hydrogen peroxide, and the metalloids antimonite, arsenite and silicic acid. Here, we summarize the available data on permeability properties and physiological settings of these aquaporins and we analyze which structural features might be connected to permeability for non-water, non-glycerol solutes. Received 31 March 2007; received after revision 3 May 2007; accepted 23 May 2007     

Biologische und chemische Wege zur Anreicherung von Spurenelementen

Summary Using as examples hemovanadin, the vanadium-containing blood pigment of the ascidianPhallusia mamillata, and ferritin, the protein for iron storage in mammals, pathways for the concentration of vanadium and of iron are described: These have been realizedin vitro and may occurin vivo. The uptake and concentration of heavy metals in nature seems to occur by means of complexing agents.High molecular weight, insoluble chelating substances which are able to bind metal ions, especially uranium and copper selectively, have been synthesized. Recovery of the metals is possible without destruction of the chelating groups, and, as in the case of ion-exchange resins, repeated cycles can be carried out without diminishing the metal-binding capacity.     

Highly reactive oxygen species: detection, formation, and possible functions

The so-called reactive oxygen species (ROS) are defined as oxygen-containing species that are more reactive than O(2) itself, which include hydrogen peroxide and superoxide. Although these are quite stable, they may be converted in the presence of transition metal ions, such as Fe(II), to the highly reactive oxygen species (hROS). hROS may exist as free hydroxyl radicals (HO·), as bound ("crypto") radicals or as Fe(IV)-oxo (ferryl) species and the somewhat less reactive, non-radical species, singlet oxygen. This review outlines the processes by which hROS may be formed, their damaging potential, and the evidence that they might have signaling functions. Since our understanding of the formation and actions of hROS depends on reliable procedures for their detection, particular attention is given to procedures for hROS detection and quantitation and their applicability to in vivo studies.     

Active-site mutants of class B beta-lactamases: substrate binding and mechanistic study

Increased resistance to β-lactam antibiotics is mainly due to β-lactamases. X-ray structures of zinc β-lactamases unraveled the coordination of the metal ions, but their mode of action remains unclear. Recently, enzymes in which one of the zinc ligands was mutated have been characterized and their catalytic activity against several β-lactam antibiotics measured. A molecular modeling study of these enzymes was performed here to explain the catalytic activity of the mutants. Coordination around the zinc ions influences the way the tetrahedral intermediate is bound; any modification influences the first recognition of the substrate by the enzyme. For all the studied mutants, at least one of the interactions fails, inducing a loss of catalytic efficiency compared to the wild type. The present studies show that the enzyme cavity is a structure of high plasticity both structurally and mechanistically and that local modifications may propagate its effects far from the mutated amino acid. Received 28 August 2002; received after revision 22 October 2002; accepted 24 October 2002 RID="*" ID="*"Corresponding author.     

Über das Verhalten von Riboflavin-Semichinon gegen Metallionen. Modellstudien zur Metall-Flavoenzymkatalyse

Summary The specific metal-chelating properties of the flavoenzymes are not to be interpreted by the metal affinities of riboflavin (Rfl) and leukoriboflavin (RflH₂), but by those of the semiquinoid radical (RflH). The reaction of RflH with metal ions gives rise to the formation of chelates that are well characterisable by potentiometric and spectrophotometric analysis. By the chelation, the semiquinoid level of the ligand is stabilised in the thermodynamic as well as in the kinetic sense.

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Ich danke Herrn Prof.H. Erlenmeyer für sein Interesse an dieser Arbeit und dem Schweizerischen Nationalfonds zur Förderung der wissenschaftlichen Forschung für materielle Unterstützung. Den Herren Prof.H. A. Harbury, Yale und Dr.H. Brintzinger, Basel, danke ich für wertvolle Diskussionen und Hinweise.     

Phtalocyanine in wässriger Lösung. Zum Mechanismus der Metallkomplexbildung

Summary The mechanism of incorporation of different mental ions into phthalocyaninetetrasulfonic acid in aqueous solution has been investigated. It was found that the rate of the reacion with Cu²⁺ depends on the dissociation rate of the N-H-bond of this porphyrin-like chelating agent, whereas the reaction rate with other metal ions, like Zn²⁺, does not.

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II. Mitt. Siehe I. Mitt.:K. Bernauer undS. Fallab, Helv.44, 1287 (1961).

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Herrn Prof. Dr.H. Erlenmeyer sind wir für sein reges Interesse an dieser Arbeit zu bestem Dank verpflichtet.