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1.
Ting Zhao 《Journal of inorganic biochemistry》2010,104(2):186-192
Mass spectrometric studies of the interactions of cisplatin and transplatin with myoglobin (Mb) provide information concerning interaction kinetics, Mb adduct identity, and cisplatin and transplatin binding sites on Mb. Although the Mb-cisplatin interaction is faster than the Mb-transplatin interaction, monoadducts and diadducts were formed in both the interactions over 30 h. In order to locate the binding sites of cisplatin and transplatin on Mb, digests of free Mb, Mb-cisplatin and Mb-transplatin adducts were subjected to analysis by Fourier transform mass spectrometry (FT-MS). This analysis revealed that two fragment ions, 1313.275+ and 1316.685+, were obtained only from the Mb-cisplatin and Mb-transplatin adduct digests. Tandem mass spectrometry (MS/MS and MS3) of the 1313.275+ and 1316.685+ ions indicate that these ions arise from [Pt(NH3)]2+ and [Pt(NH3)2]2+, respectively, bound to peptide His97-Gly153. The product-ion spectra of the MS/MS and MS3 analyses of the 1313.275+ ion indicate a common binding site of cisplatin and transplatin on His116-His119 residues. The interactions of cisplatin and transplatin with a dipeptide His-Ser and the three dimensional (3D) structure of native Mb suggest that cisplatin and transplatin coordinate to His116 and His119. 相似文献
2.
The aggregation of α-synuclein (α-Syn), the major component of intracellular Lewy body inclusions in dopaminergic neurons of the substantia nigra, plays a critical role in the etiology of Parkinson disease (PD). Long-term effects of redox-active transition metals (Cu, Fe) and oxidative chemical imbalance underlie the disease progression and neuronal death. In this work, we provide evidence that a brain metalloprotein, Zn7-metallothionein-3 (Zn7MT-3), possesses a dynamic role in controlling aberrant protein–copper interactions in PD. We examined the properties of the α-Syn–Cu(II) complex with regard to molecular oxygen, the biological reducing agent ascorbate, and the neurotransmitter dopamine. The results revealed that under aerobic conditions α-Syn–Cu(II) possesses catalytic oxidase activity. The observed metal-centered redox chemistry significantly promotes the production of hydroxyl radicals and α-Syn oxidation and oligomerization, processes considered critical for cellular toxicity. Moreover, we show that Zn7MT-3, through Cu(II) removal from the α-Syn–Cu(II) complex, efficiently prevents its deleterious redox activity. We demonstrate that the Cu(II) reduction by thiolate ligands of Zn7MT-3 and the formation of Cu(I)4Zn4MT-3, in which an unusual oxygen-stable Cu(I)4–thiolate cluster is present, comprise the underlying molecular mechanism by which α-Syn and dopamine oxidation, α-Syn oligomerization, and ROS production are abolished. These studies provide new insights into the bioinorganic chemistry of PD. 相似文献
3.
DNA–protein cross-links are formed by various DNA-damaging agents including antitumor platinum drugs. The natures of these ternary DNA–Pt–protein complexes (DPCLs) can be inferred, yet much remains to be learned about their structures and mechanisms of formation. We investigated the origin of these DPCLs and their cellular processing on molecular level using gel electrophoresis shift assay. We show that in cell-free media cisplatin [cis-diamminedichloridoplatinum(II)] forms DPCLs more effectively than ineffective transplatin [trans-diamminedichloridoplatinum(II)]. Mechanisms of transformation of individual types of plain DNA adducts of the platinum complexes into the DPCLs in the presence of several DNA-binding proteins have been also investigated. The DPCLs are formed by the transformation of DNA monofunctional and intrastrand cross-links of cisplatin. In contrast, interstrand cross-links of cisplatin and monofunctional adducts of transplatin are stable in presence of the proteins. The DPCLs formed by cisplatin inhibit DNA polymerization or removal of these ternary lesions from DNA by nucleotide excision repair system more effectively than plain DNA intrastrand or monofunctional adducts. Thus, the bulky DNA–protein cross-links formed by cisplatin represent a more distinct and persisting structural motif recognized by the components of downstream cellular systems processing DNA damage considerably differently than the plain DNA adducts of this metallodrug. 相似文献
4.
Magnus Jensen Morten Bjerring Niels Chr. Nielsen Willy Nerdal 《Journal of biological inorganic chemistry》2010,15(2):213-223
Cisplatin [cis-diamminedichloridoplatinum(II)] is used in chemotherapy where platinum–DNA adducts initiate tumor cell death. It is possible
that side effects such as neurotoxicity and cellular cisplatin resistance can be due to interaction of cisplatin with lipids
and the phospholipid bilayer. In this study, 13C, 31P, and 15N solid-state NMR spectra of 1-palmitoyl-2-oleoyl phosphatidylserine (POPS) bilayers, POPS bilayers with 10 mol% cisplatin,
and POPS bilayers with 30 mol% cisplatin were acquired. In addition, 15N{31P} rotational echo double resonance spectra of POPS bilayers with 30 mol% cisplatin were acquired. The data demonstrate that
the serine head group of phosphatidylserine binds to the aquated form of cisplatin and that cisplatin release of ammine takes
place. It appears that the cisplatin release of ammine is followed by another cisplatin–POPS complex formation, possibly with
cisplatin binding to one of the oxygen atoms of the POPS phosphate moiety. 相似文献
5.
trans -dichloroplatinum(II) complexes exhibit antitumor activity violate the classical structure-activity relationships of platinum(II)
complexes. These novel “nonclassical”trans platinum complexes also comprise those containing planar aromatic amines. Initial studies have shown that these compounds
form a considerable amount of DNA interstrand cross-links (up to ∼30%) with a rate markedly higher than clinically ineffective
transplatin. The present work has shown, using Maxam-Gilbert footprinting, that trans-[PtCl2(NH3)(quinoline)] and trans-[PtCl2(NH3)(thiazole)], representatives of the group of new antitumor trans-dichloroplatinum complexes containing planar amines, preferentially form DNA interstrand cross-links between guanine residues
at the 5′-GC-3′ sites. Thus, DNA interstrand cross-linking by trans-[PtCl2(NH3)(quinoline)] and trans-[PtCl2(NH3)(thiazole)] is formally equivalent to that by antitumor cisplatin, but different from clinically ineffective transplatin
which preferentially forms these adducts between complementary guanine and cytosine residues. This result shows for the first
time that simple chemical modification of the structure of an inactive compound alters its DNA binding site into a DNA adduct
of an active drug.
Received: 6 January 2000 / Accepted: 8 March 2000 相似文献
6.
Tereza Suchánková Marie Vojtíšková Jan Reedijk Viktor Brabec Jana Kašpárková 《Journal of biological inorganic chemistry》2009,14(1):75-87
The global modification of mammalian and plasmid DNAs by the novel platinum compounds cis-[PtCl2(isopropylamine)(1-methylimidazole)] and trans-[PtCl2(isopropylamine)(1-methylimidazole)] and the reactivity of these compounds with reduced glutathione (GSH) were investigated
in cell-free media using various biochemical and biophysical methods. Earlier cytotoxicity studies had revealed that the replacement
of the NH3 groups in cisplatin by the azole and isopropylamine ligands lowers the activity of cisplatin in both sensitive and resistant
cell lines. The results of the present work show that this replacement does not considerably affect the DNA modifications
by this drug, recognition of these modifications by HMGB1 protein, their repair, and reactivity of the platinum complex with
GSH. These results were interpreted to mean that the reduced activity of this analog of cisplatin in tumor cell lines is due
to factors that do not operate at the level of the target DNA. In contrast, earlier studies had shown that the replacement
of the NH3 groups in the clinically ineffective trans isomer (transplatin) by the azole and isopropylamine ligands results in a radical enhancement of its activity in tumor cell
lines. Importantly, this replacement also markedly alters the DNA binding mode of transplatin, which is distinctly different
from that of cisplatin, but does not affect reactivity with GSH. Hence, the results of the present work are consistent with
the view and support the hypothesis systematically tested by us and others that platinum drugs that bind to DNA in a fundamentally
different manner from that of conventional cisplatin may have altered pharmacological properties. 相似文献
7.
Chak Ming Sze George N. Khairallah Zhiguang Xiao Paul S. Donnelly Richard A. J. O’Hair Anthony G. Wedd 《Journal of biological inorganic chemistry》2009,14(2):163-165
The chaperone protein CopC from Pseudomonas syringae features high-affinity binding sites (K
D ~ 10−13 M) for both CuI (Met-rich) and CuII (His-rich). When presented with these sites in the apoprotein, electrospray ionisation mass spectrometry confirmed that cis-Pt(NH3)2Cl2 (cisplatin) and the fragments [PtIIL]2+ (L is 1,2-diaminoethane, 2,2′-bipyridine) occupied the CuI site specifically in the 1:1 Pt–CopC adducts (purified by cation-exchange chromatography). The cis-Pt(NH3)2 fragment was not present in these adducts (the dominant product for cisplatin was Pt–CopC in which all original ligands were
displaced), while bidentate ligands L were retained in LPt–CopC adducts. In the context of the Met-rich CuI pump Ctr1 as a significant entry point for cisplatin into mammalian cells, the present work confirms the ability of Met-rich
sites in proteins to remove all ligands from cisplatin. It focuses attention on the potential of proteins that are part of
the natural copper transport pathways to sequester the drug. These pathways are worthy of further study at the molecular level.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
8.
The effect of nitric oxide on metal release from metallothionein-3: gradual unfolding of the protein
Hui Wang Hongyan Li Bin Cai Zhong-Xian Huang Hongzhe Sun 《Journal of biological inorganic chemistry》2008,13(3):411-419
Metallothionein-3 (MT-3), or neuronal growth inhibitory factor, which exhibits growth inhibitory activity, is a brain-specific
metallothionein. In this study, the effect of nitric oxide (NO) on metal release (using Cd2+ as a probe) from MT-3 was examined by 113Cd and 2D [1H–15N] heteronuclear single-quantum coherence NMR spectroscopy. The exposure of human MT-3 to NO leads to a nonselective release
of the three metals from the β-domain. In contrast to metallothionein-1 and metallothionein-2, two of the bound metals in
the α-domain were also partially released, with the domain structure remaining almost unchanged. Further addition of NO resulted
in the complete release of metals and concomitant unfolding of the protein. The preference of release of the two metals in
the α-domain was attributed to the presence of two slightly different coordination environments for the four cadmium/zinc
atoms. 相似文献
9.
Mammalian metallothioneins (
\textM7\textIIMTs {\text{M}}_7^{\text{IIMTs}} ) show a clustered arrangement of the metal ions and a nonregular protein structure. The solution structures of Cd3-thiolate cluster containing β-domain of mouse β-MT-1 and rat β-MT-2 show high structural similarities, but widely differing
structure dynamics. Molecular dynamics simulations revealed a substantially increased number of
\textNH - \textSg {\text{NH - }}{{\text{S}}^\gamma } hydrogen bonds in β-MT-2, features likely responsible for the increased stability of the Cd3-thiolate cluster and the enfolding protein domain. Alterations in the
\textNH - \textSg {\text{NH - }}{{\text{S}}^\gamma } hydrogen-bonding network may provide a rationale for the differences in dynamic properties encountered in the β-domains of
MT-1, -2, and -3 isoforms, believed to be essential for their different biological function. 相似文献
10.
Zhengyi Wu Qin Liu Xiao Liang Xiaoliang Yang Ningyan Wang Xinghao Wang Hongzhe Sun Yi Lu Zijian Guo 《Journal of biological inorganic chemistry》2009,14(8):1313-1323
Cellular uptake of platinum-based antitumor drugs is a critical step in the mechanism of the drug action and associated resistance,
and deeper understanding of this step may inspire development of novel methods for new drugs with reduced resistance. Human
copper transporter 1 (hCtr1), a copper influx protein, was recently found to facilitate the cellular entry of several platinum
drugs. In the work reported here, we constructed a Met- and His-rich 20mer peptide (hCtr1-N20) corresponding to the N-terminal
domain of hCtr1, which is the essential domain of hCtr1 for transporting platinum drugs. The interactions of the peptide with
cisplatin and its analogues, including transplatin, carboplatin, oxaliplatin, and [Pt(l-Met)Cl2], were explored at the molecular level. Electrospray ionization (ESI) mass spectrometry (MS) data revealed that all of the
platinum(II) complexes used in present study can bind to hCtr1-N20 in 1:1 and 2:1 stoichiometry. Four Met residues should
be involved in binding to cis-platinum complexes on the basis of the tandem MS spectrometry and previously reported data. Time-dependent 2D [1H,15N] heteronuclear single quantum coherence NMR spectra indicate the reaction of cisplatin with hCtr1-N20 is a stepwise process.
The intermediate, however, is transient, which is consistent with the ESI-MS results. Time-dependent ESI-MS data revealed
that the geometry and the properties of both the leaving and the nonleaving groups of platinum(II) complexes play essential
roles in controlling the reactivity and formation of the final products with hCtr1-N20. 相似文献
11.
Giuseppe Digilio Chiara Bracco Laura Vergani Mauro Botta Domenico Osella Aldo Viarengo 《Journal of biological inorganic chemistry》2009,14(2):167-178
The metal–thiolate connectivity of recombinant Cd7-MT10 metallothionein from the sea mussel Mytilus galloprovincialis has been investigated for the first time by means of multinuclear, multidimensional NMR spectroscopy. The internal backbone
dynamics of the protein have been assessed by the analysis of 15N T
1 and T
2 relaxation times and steady state {1H}–15N heteronuclear NOEs. The 113Cd NMR spectrum of mussel MT10 shows unique features, with a remarkably wide dispersion (210 ppm) of 113Cd NMR signals. The complete assignment of cysteine Hα and Hβ proton resonances and the analysis of 2D 113Cd–113Cd COSY and 1H–113Cd HMQC type spectra allowed us to identify a four metal–thiolate cluster (α-domain) and a three metal–thiolate cluster (β-domain),
located at the N-terminal and the C-terminal, respectively. With respect to vertebrate MTs, the mussel MT10 displays an inversion
of the α and β domains inside the chain, similar to what observed in the echinoderm MT-A. Moreover, unlike the MTs characterized
so far, the α-domain of mussel Cd7-MT10 is of the form M4S12 instead of M4S11, and has a novel topology. The β-domain has a metal–thiolate binding pattern similar to other vertebrate MTs, but it is conformationally
more rigid. This feature is quite unusual for MTs, in which the β-domain displays a more disordered conformation than the
α-domain. It is concluded that in mussel Cd7-MT10, the spacing of cysteine residues and the plasticity of the protein backbone (due to the high number of glycine residues)
increase the adaptability of the protein backbone towards enfolding around the metal–thiolate clusters, resulting in minimal
alterations of the ideal tetrahedral geometry around the metal centres. 相似文献
12.
Clinically ineffective transplatin [trans-diamminedichloridoplatinum(II)] is used in the studies of the structure-pharmacological activity relationship of platinum compounds. In addition, a number of transplatin analogs exhibit promising toxic effects in several tumor cell lines including those resistant to conventional antitumor cisplatin. Moreover, transplatin-modified oligonucleotides have been shown to be effective modulators of gene expression. Owing to these facts and because DNA is also considered the major pharmacological target of platinum complexes, interactions between transplatin and DNA are of great interest. We examined, using biophysical and biochemical methods, the stability of 1,3-GNG intrastrand cross-links (CLs) formed by transplatin in short synthetic oligodeoxyribonucleotide duplexes and natural double-helical DNA. We have found that transplatin forms in double-helical DNA 1,3-GNG intrastrand CLs, but their stability depends on the sequence context. In some sequences the 1,3-GNG intrastrand CLs formed by transplatin in double-helical DNA readily rearrange into interstrand CLs. On the other hand, in a number of other sequences these intrastrand CLs are relatively stable. We show that the stability of 1,3-GNG intrastrand CLs of transplatin correlates with the extent of conformational distortion and thermodynamic destabilization induced in double-helical DNA by this adduct. 相似文献
13.
Yousef Najajreh Jana Kasparkova Victoria Marini Dan Gibson Viktor Brabec 《Journal of biological inorganic chemistry》2005,10(7):722-731
trans-Diaminedicholoroplatinum(II) complexes with one planar and one non-planar heterocyclic amine ligand were designed as new potential antitumor drugs. The X-ray crystallographic structures of trans-[PtCl2(4-picoline)(piperidine)] and trans-[PtCl2(4-picoline)(piperazine)]·HCl revealed that the piperidine and piperazine ligands bind to the platinum through the equatorial position and that the ligands adopt the chair conformation. The nonplatinated amine of the piperazine can form hydrogen bonds with atoms that are approximately 7.5 Å away from the Pt binding site. DNA is considered a major pharmacological target of platinum compounds. Hence, to expand the database correlating structural features of platinum compounds and DNA distortions induced by these compounds, which may facilitate identification of more effective anticancer platinum drugs, we describe the DNA binding mode in a cell-free medium of trans-[PtCl2(4-picoline)(piperidine)] and trans-[PtCl2(4-picoline)(piperazine)]·HCl. Interestingly, the overall impact of the replacement of the second ammine group in transplatin by the heterocyclic ligands appears to change the character of the global conformational changes induced in DNA towards that induced by cisplatin. The clinical ineffectiveness of the parent transplatin has been proposed to be also associated with its reduced capability to form bifunctional adducts in double-helical DNA. The results of the present work support the view that replacement of both ammine groups of transplatin by heterocyclic ligands enhances cytotoxicity probably due to the marked enhancement of the stability of intrastrand cross-links in double-helical DNA. 相似文献
14.
Anna Halmikov Pavla Heringov Jana Kaprkov Francesco P. Intini Giovanni Natile Alina Nemirovski Dan Gibson Viktor Brabec 《Journal of inorganic biochemistry》2008,102(5-6):1077
Cytotoxicity and mutagenicity of trans,trans,trans-[PtCl2(CH3COO)2(NH3)(1-adamantylamine)] [trans-adamplatin(IV)] and its reduced analog trans-[PtCl2(NH3)(1-adamantylamine)] [trans-adamplatin(II)] were examined. In addition, the several factors underlying biological effects of these trans-platinum compounds using various biochemical methods were investigated. A notable feature of the growth inhibition studies was the remarkable circumvention of both acquired and intrinsic cisplatin resistance by the two lipophilic trans-compounds. Interestingly, trans-adamplatin(IV) was considerably less mutagenic than cisplatin. Consistent with the lipophilic character of trans-adamplatin complexes, their total accumulation in A2780 cells was considerably greater than that of cisplatin. The results also demonstrate that trans-adamplatin(II) exhibits DNA binding mode markedly different from that of ineffective transplatin. In addition, the reduced deactivation of trans-adamplatin(II) by glutathione seems to be an important determinant of the cytotoxic effects of the complexes tested in the present work. The factors associated with cytotoxic and mutagenic effects of trans-adamplatin complexes in tumor cell lines examined in the present work are likely to play a significant role in the overall antitumor activity of these complexes. 相似文献
15.
Montserrat Serra-Batiste Neus Cols Luis A. Alcaraz Antonio Donaire Pilar González-Duarte Milan Vašák 《Journal of biological inorganic chemistry》2010,15(5):759-776
Most crustacean metallothioneins (MTs) contain 18 Cys residues and bind six divalent metal ions. The copper-specific CuMT-2
(MTC) of the blue crab Callinectes sapidus with 21 Cys residues, of which six are organized in two uncommon Cys-Cys-Cys sequences, represents an exception. However,
its metal-binding properties are unknown. By spectroscopic and spectrometric techniques we show that all 21 Cys residues of
recombinant MTC participate in the binding of Cu(I), Zn(II), and Cd(II) ions, indicating that both Cys triplets act as ligands.
The fully metallated M8
II–MTC (M is Zn, Cd) form possesses high- and low-affinity metal binding sites, as evidenced by the formation of Zn6–MTC and Cd7–MTC species from M8
II–MTC after treatment with Chelex 100. The NMR characterization of Cd7–MTC suggests the presence of a two-domain structure, each domain containing one Cys triplet and encompassing either the three-metal
or the four-metal thiolate cluster. Whereas the metal–Cys connectivities in the three-metal cluster located in the N-terminal
domain (residues 1–31) reveal a Cd3Cys9 cyclohexane-like structure, the presence of dynamic processes in the C-terminal domain (residues 32–64) precluded the determination
of the organization of the four-metal cluster. Absorption and circular dichroism features accompanying the stepwise binding
of Cu(I) to MTC suggest that all 21 Cys are involved in the binding of eight to nine Cu(I) ions (Cu8–9–MTC). The subsequent generation of Cu12–MTC involves structural changes consistent with a decrease in the Cu(I) coordination number. Overall, the metal-binding properties
of MTC reported here contribute to a better understanding of the role of Cys triplets in MTs. 相似文献
16.
Michaela Frybortova Olga Novakova Viktor Brabec 《Journal of biological inorganic chemistry》2014,19(7):1203-1208
Oligonucleotides modified by clinically ineffective trans-diamminedichloridoplatinum(II) (transplatin) have been shown to be effective modulators of gene expression. This is so because in some nucleotide sequences the 1,3-GNG intrastrand adducts formed by transplatin in double-helical DNA readily rearrange into interstrand cross-links so that they can cross-link the oligonucleotides to their targets. On the other hand, in a number of other sequences these intrastrand adducts are relatively stable, which represents the major difficulty in the clinical use of the antisense transplatin-modified oligonucleotides. Therefore, we examined in this study, the stability of 1,3-GNG intrastrand adducts in double-helical DNA formed by a new antitumor derivative of transplatin, trans-[Pt(CH3NH2)2Cl2], in the sequence contexts in which transplatin formed relatively stable intrastrand cross-links which did not readily rearranged into interstrand cross-links. We have found that 1,3-GNG intrastrand adducts in double-helical DNA formed by trans-[Pt(CH3NH2)2Cl2] even in such sequences readily rearrange into interstrand cross-links. This work also suggests that an enhanced frequency of intrastrand cross-links yielded by trans-[Pt(CH3NH2)2Cl2] is a consequence of the fact that these DNA lesions considerably distort double-helical DNA in far more sequence contexts than parent transplatin. Our results suggest that trans-[Pt(CH3NH2)2Cl2]-modified oligonucleotides represent promising candidates for new agents in antisense or antigene approach. 相似文献
17.
18.
E. V. Navolotskaya T. A. Zargarova T. N. Lepikhova V. L. Turobov R. I. Nurieva N. V. Malkova V. P. Zav’yalov V. M. Lipkin 《Russian Journal of Bioorganic Chemistry》2000,26(1):27-33
The antiproliferative and immunosuppressivein vitro effects ofimmunocortin, a synthetic adrenocorticotropin-like (ACTH-like) decapeptide H-Val-Lys-Lys-Pro-Gly-Ser-Ser-Val-Lys-Val-OH, whose sequence
corresponds to segment 11–20 of the variable part of the human IgG1 heavy chain, were studied. At concentrations of 10−11−10−7 M, immunocortin was found to inhibit the growth of the human MT-4 T-lymphoblastoid cell line, to suppress the blast transformation
of thymocytes, and to decrease the spontaneous mobility of peritoneal macrophages and their bactericidal action toward the
virulent strainSalmonella typhimurium 415. By using a125I-labeled “addressing” fragment of ACTH {[125I]ACTH (13–24)}, we showed that MT-4 cells express specific receptors for ACTH (K
d 97 pM). Immunocortin and human ACTH (but not the heavy chain of IgG1) competitively inhibited the binding of [125I]ACTH-(13–24) to these receptors withK
i1 of 0.38 andK
i2 of 0.34 nM, respectively. Specific receptors for ACTH (K
d 5.8 nM) on mouse thymocytes were detected and characterized. The unlabeled immunocortin was shown to compete with labeled
ACTH-(13–24) for binding to these receptors (K
i=1.8 nM), and this binding of immunocortin to receptors on thymocytes activates adenylate cyclase from these cells and increases
the intracellular concentration of cAMP. 相似文献
19.
The thermodynamics of cisplatin and transplatin hydration is studied within the model of constant pH solution. Several implicit
solvation models were chosen for the determination of pKa and pK constants of the hydration reactions. The polarizable dielectric model (DPCM), integral equation formalism polarizable
model (IEFPCM), and polarizable conductor model (CPCM) were combined with the ‘united atom model for Hartree-Fock’ (UAHF)
method for cavity construction and the B3LYP/6-31++G(2dp,2pd) level of calculations for the determination of electronic energies.
The results were compared with the COSMO-RS and SM8 model developed by Truhlar (with M06 and MPWX functionals and the charge
model CM4). The RMS difference between experimental and calculated pKa values of cis/transplatin, water, HCl, and NH4+ was used to evaluate accuracy of calculations. The DPCM model was confirmed to perform the best. The predicted pKa constants were used in Legendre transformation for the estimation of the ΔG’ energies in the constant-pH model. The dependence
of the pK constant on pH is plotted and compared with experimental value at pH=7.4. The influence of various chloride concentrations
on the molar fractions of dissolved forms of cisplatin is examined for the DPCM model. The increased ratio of cisplatin active
aqua-forms is clearly visible for 4 mM chloride solution in comparison with 104 mM Cl- concentration. 相似文献
20.
Duncan E.K. SutherlandKelly L. Summers Martin J. Stillman 《Biochemical and biophysical research communications》2012,426(4):601-607
Mammalian metallothioneins (MTs) are a family of small cysteine rich proteins believed to have a number of physiological functions, including both metal ion homeostasis and toxic metal detoxification. Mammalian MTs bind 7 Zn2+ or Cd2+ ions into two distinct domains: an N-terminal β-domain that binds 3 Zn2+ or Cd2+, and a C-terminal α-domain that binds 4 Zn2+ or Cd2+. Although stepwise metalation to the saturated M7-MT (where M = Zn2+ or Cd2+) species would be expected to take place via a noncooperative mechanism involving the 20 cysteine thiolate ligands, literature reports suggest a cooperative mechanism involving cluster formation prior to saturation of the protein. Electrospray ionization mass spectrometry (ESI-MS) provides this sensitivity through delineation of all species (Mn-MT, n = 0-7) coexisting at each step in the metalation process. We report modeled ESI-mass spectral data for the stepwise metalation of human recombinant MT 1a (rhMT) and its two isolated fractions for three mechanistic conditions: cooperative (where the binding affinities are: K1 < K2 < K3 < ··· < K7), weakly cooperative (where K1 = K2 = K3 = ··· = K7), and noncooperative, (where K1 > K2 > K3 > ··· > K7). Detailed ESI-MS metalation data of human recombinant MT 1a by Zn2+ and Cd2+ are also reported. Comparison of the experimental data with the predicted mass spectral data provides conclusive evidence that metalation occurs in a noncooperative fashion for Zn2+ and Cd2+ binding to rhMT 1a. 相似文献