ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Kinetics of reversible N-ethylmaleimide alkylation of metallothionein and the subsequent metal release (1997)
    Springer
    JBIC 2 (1997), S. 65-73 
    Details
    ISSN: 1432-1327
    Keywords: Key words Metallothionein ; N-Ethylmaleimide ; Alkylation ; Kinetics and mechanism ; 111Cd-NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  The model alkylating agent N-ethylmaleimide (NEM) reacts reversibly at the metal-bound thiolates of Zn7MT and Cd7MT. An unprecedented feature of this reaction is that it approaches equilibrium and requires a large excess of NEM (〉1 mM for 3 μM protein) to drive it to completion. The complex kinetics of the reaction can be followed by monitoring the release of bound metal ions using the metallochromic dyes Zincon (ZI) for Zn7MT and pyridylazoresorcinol for Cd7MT. An initial lag phase is followed by more rapid release of zinc ions. The observed pseudo-first-order rate constants for the two phases are independent of the ZI and Zn7MT concentrations. The complex NEM concentration dependence of each phase, k f, obs=k f 1+k f 2 [NEM] and k s, obs=k s 1+k s 2 [NEM], demonstrates that the forward reactions are second order and the reverse reactions are first order. The alkylation can be reversed using 2-mercaptoethanol to compete for the protein-bound NEM and regenerate the Zn-binding capability of alkylated MT. An explanation of these observations, based on the reversibility of cysteine alkylation by NEM, was developed and tested. The reactions of Cd7MT are less complete than those of Zn7MT and occur more slowly. 111Cd-NMR studies of the partially alkylated 111Cd7MT reveal that reaction with only four equivalents of NEM completely alters the cluster structure and eliminates the spectral signatures of the α and β clusters, although very little cadmium has been removed from the protein. This finding substantiates the proposed kinetic intermediate, a partially alkylated MT with complete or nearly complete retention of the metal ions, and rules out the possibility of cooperative reactions at either cluster.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050107
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Equilibrium binding constants and facile dissociation of novel serum albumin-dicyanoaurate(I) complexes (1998)
    Springer
    JBIC 3 (1998), S. 9-17 
    Details
    ISSN: 1432-1327
    Keywords: Key words Dicyanoaurate(I) ; Bovine serum albumin ; Equilibrium binding constants ; 13C NMR ; Labile dissociation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  Dicyanoaurate(I), Au(CN)2 –, an important metabolite of chrysotherapy agents (anti-arthritic gold drugs), contains two tightly bound cyanide ligands which render it relatively unreactive toward ligand exchange reactions with potential gold-binding ligands. The extent and nature of its binding to bovine serum albumin (BSA), which may modulare the in vivo activity of Au(CN)2 –, were investigated to determine whether Au(CN)2 – might be more bioavailable than other gold complexes. 13C NMR spectroscopy, radioisotope tracers, chromatography, ultrafiltration, and atomic spectroscopy, employing Au(13CN)2 – or Au(14CN)2 – as appropriate, revealed two distinct binding mechanisms. The dominant reaction is reversible association (non-specific binding) of intact Au(CN)2 – ions to form BSA·[Au(CN)2 –] n adducts. Approximately one equivalent binds with an equilibrium binding constant (pH 7.4, 25  °C) of K 1=5.5 (±1.1)×104, and three additional equivalents bind with a constant of 7.0 (±0.1)×103. Au(13CN)2 – associated with albumin is characterized by a broad 13C NMR resonance at δC=154.7 ppm compared to the sharp resonance of the free complex at 156.4 ppm. The BSA·[Au(CN)2 –] n adducts readily dissociate during gel exclusion chromatography and are therefore underestimated, but are retained and accurately quantitated by ultrafiltration methods. The second binding mechanism is a ligand exchange reaction at Cys-34, to form AlbSAuCN, which accounts for only a small fraction (≤11%) of the bound gold. The small extent of the latter interaction differentiates Au(CN)2 – from the gold drugs such as auranofin, aurothiomalate (Myochrysin) and aurothioglucose (Solganol), which undergo ligand exchange at Cys-34 of albumin to form tightly bound gold-protein complexes. The weak interaction at Cys-34 and the facile dissociation of bound, intact Au(CN)2 – are consistent with its putative role as a gold metabolite that can be accumulated intracellularly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050203
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Characterization of the cadmium complex of peptide 49–61: a putative nucleation center for cadmium-induced folding in rabbit liver metallothionein IIA (1999)
    Springer
    JBIC 4 (1999), S. 495-507 
    Details
    ISSN: 1432-1327
    Keywords: Key words Metallothionein ; Peptide-metal complexes ; 111Cd NMR ; Protein folding ; Molecular mechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  The synthetic peptide fragment containing residues 49–61 of rabbit liver metallothionein II (MT-II) (Ac-Ile-Cys-Lys-Gly-Ala-Ser-Asp-Lys-Cys-Ser-Cys-Cys-Ala-COOH), which includes the only sequential four cysteines bound to the same metal ion in Cd7MT, forms a stable, monomeric Cd-peptide complex with 1 : 1 stoichiometry (Cd:peptide) via Cd-thiolate interactions. This represents the first synthesis of a single metal-binding site of MT independent of the domains. The 111Cd NMR chemical shift at 716 ppm indicates that the 111Cd2+ in the metal site is terminally coordinated to four side-chain thiolates of the cysteine residues. The pH of half dissociation for this Cd-peptide derivative, ∼3.3, demonstrates an affinity similar to that for Cd7MT. Molecular mechanics calculations show that the thermodynamically most stable folding for this isolated Cd2+ center has the same counterclockwise chirality (Λ or S) observed in the native holo-protein. These properties are consistent with its proposed role as a nucleation center for cadmium-induced protein folding. However, the kinetic reactivity of the CdS4 structure toward 5,5′-dithiobis(5-nitrobenzoate) (DTNB) and EDTA is greatly increased compared to the complete cluster (α-domain or holo-protein). The rate law for the reaction with DTNB is rate=(k uf +k 1,f +k 2,f [DTNB])[peptide], where k uf=0.15 s–1, k 1,f=2.59×10–3 s–1, and k 2,f=0.88 M–1 s–1. The ultrafast step (uf), observable only by stopped-flow measurement, is unprecedented for mammalian (M7MT) and crustacean (M6MT) holo-proteins or the isolated domains. The accommodation of other metal ions by the peptide indicates a rich coordination chemistry, including stoichiometries of M-peptide for Hg2+, Cd2+, and Zn2+, M2-peptide for Hg2+ and Au+, and (Et3PAu)2-peptide.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050335
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...