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At least 991 records · Page 55Linked to original sources
PubMed2005

Synthesis, spectroscopy and antiproliferative activity of cis- and trans-platinum(II) complexes with diethyl (pyridin-4-ylmethyl)phosphate. X-ray crystal structure of trans-Pt(II) complex.

Preparations of cis- and trans-platinum(II) complexes of diethyl (pyridin-4-ylmethyl)phosphate (4-pmOpe) have been described. These complexes were identified and characterized by far-IR, 1H NMR, 13C NMR, 31P NMR and 195Pt NMR and microanalyses. The crystal and molecular structure of trans-platinum(II) complex i.e., trans-[PtCl2(4-pmOpe)2] was determined by the X-ray diffraction. Novel complexes were assayed for their potential antiproliferative effect against HT 29 (colorectal adenocarcinoma) and A 549 (non-small cell lung cancer) cell lines as well as normal human peripheral blood lymphocytes. The results obtained indicate that novel analogues of cis-diamminedichloroplatinum(II) cause inhibition of cells growth which suggest that they could be chemotherapeutic drugs in the future.

Adenocarcinoma↗
PubMed2006

Nonheme iron(II) complexes of macrocyclic ligands in the generation of oxoiron(IV) complexes and the catalytic epoxidation of olefins.

Mononuclear nonheme oxoiron(IV) complexes bearing 15-membered macrocyclic ligands were generated from the reactions of their corresponding iron(II) complexes and iodosylbenzene (PhIO) in CH(3)CN. The oxoiron(IV) species were characterized with various spectroscopic techniques such as UV-vis spectrophotometer, electron paramagnetic resonance, electrospray ionization mass spectrometer, and resonance Raman spectroscopy. The oxoiron(IV) complexes were inactive in olefin epoxidation. In contrast, when iron(II) or oxoiron(IV) complexes were combined with PhIO in the presence of olefins, high yields of epoxide products were obtained. These results indicate that in addition to the oxoiron(IV) species, there must be at least one more active oxidant (e.g., Fe(IV)-OIPh adduct or oxoiron(V) species) that effects the olefin epoxidation. We have also demonstrated that the ligand environment of iron catalysts is an important factor in controlling the catalytic activity as well as the product selectivity in the epoxidation of olefins by PhIO.

Alkenes↗
PubMed2005

Temporal fluctuation of nuclear pore complex localization by single diffusing mRNP complexes.

There is now compelling evidence that messenger ribonucleoprotein (mRNP) complexes after the release from the transcription/processing sites execute essentially unhindered Brownian movements in the nucleoplasm and target nuclear pore complexes (NPCs) by chance encounter. For the majority of genes expressed in eukaryotic cells, only single/few transcript copies are generated, which reinforces the stochastic nature of NPC localization. In this paper, I analyse the NPC localization by freely diffusing single mRNPs and discuss the implications for the temporal progression of gene expression and consecutive processes associated with the gene products. To this end, a walk-and-capture model is considered, assuming a spherical nuclear compartment with a partially absorbing boundary. Perfect absorption and perfect reflection mark the extreme outcomes. For this model, the closed-form analytic solution of the first-passage time probability density function (FPT p.d.f.), the mean passage time and variance have been obtained. The FPT p.d.f. enables to calculate the probability that single mRNPs localize the nuclear boundary and dock to NPCs within certain time windows. For freely moving mRNP complexes in osteosarcoma cell nuclei, a mean apparent diffusion coefficient (D) of 0.04 microm2 s(-1) (range 0.01-0.09 microm2 s(-1)) has been reported. Assuming a nuclear radius of 8 microm and D=0.04 microm2 s(-1), the position-averaged minimum mean passage time min for the considered model is 1.8 min, which presupposes perfect absorption of the mRNP complex at the first encounter with the nuclear boundary. In this case, the probability of capture in the time interval (0, min) is 0.67. In smaller sized yeast cell nuclei with a radius of 0.8 mum and D=0.04 microm2 s(-1), single diffusing mRNPs would localize an NPC within tens of seconds, rather than minutes.

Active Transport, Cell Nucleus↗
PubMed2006

Protein-bound dinitrosyl-iron complexes appearing in blood of rabbit added with a low-molecular dinitrosyl-iron complex: EPR studies.

The formation of protein-bound dinitrosyl-iron complexes (DNIC) in blood plasma and packed red cell fraction has been demonstrated by the EPR method in the experiments on rabbits which were i/v injected with the low-molecular DNIC with thiosulphate. This formation was ensured by transfer of Fe(+)(NO(+))(2) moieties from low-molecular DNIC onto serum albumin or hemoglobin molecules. Protein-bound DNICs appeared immediately after low-molecular DNIC injection followed with gradually decreasing their amounts. The complexes could be detected by EPR technique during more than two days. The addition of water-soluble NO scavenger, the iron complex with N-methyl-d-glucamine dithiocarbamate (MGD) resulted in decomposition of a part of protein-bound DNICs and in effective excretion of secondary products (mainly mononitrosyl-iron complexes with MGD) from the blood flow.

Animals↗
PubMed2006

Solid and solution NMR studies of the complexation of Ag+ with the trans isomer of captopril: biological activities of this high blood pressure drug along with its Ag+ complex.

Complexation of Ag(+) with captopril, 1-[(2S)-3-mercapto-2-methylpropionyl]-L-proline, has been studied by (1)H and (13)C-NMR spectroscopy. The equilibrium constants for the trans to cis isomers of captopril bound to Ag(+) were measured by (1)H NMR spectroscopy. It is observed that the trans isomer of the drug binds more strongly to Ag(+) between pH 5 and 8, as shown by the broadening of the trans isomer's resonances in (13)C NMR spectra on complexation. A monodentate complexation of the trans captopril with Ag(+) via the thiol site is proposed based on the solid-state NMR and IR data. A superior antimicrobial activity is exhibited by the Cap-Ag(I) complex compared to captopril ligand itself against Heterotrotropic Plate Counts (HPC), Pseudomonas aeruginosa and Fecal streptococcus bacteria.

Anti-Infective Agents↗
PubMed2004

Simian virus 40 infection disrupts p130-E2F and p107-E2F complexes but does not perturb pRb-E2F complexes.

In its native host species, the Rhesus Macaque, simian virus 40 (SV40) forms a persistent infection in the kidneys with no apparent harmful side effects. We show that SV40 infection of growth-arrested monkey kidney epithelial cells results in the specific disruption of certain Rb-E2F family complexes. Throughout the course of infection, p130-E2F and p107-E2F complexes are disrupted, but surprisingly pRb-E2F complexes remain intact. This suggests that the presence of some pRb-E2F complexes is not inhibitory to productive infection. Additionally, while a decrease of p130 steady state levels is observed during the later time points of infection, early during infection, p130 is readily detectable. This suggests SV40 infection overrides p130-mediated growth arrest through a mechanism(s) in addition to the well-documented T antigen-mediated degradation of p130. Finally, infection induces a dramatic relocalization of E2F4 from the nucleus to the cytoplasm. The implications of these observations to the life cycle of the virus are addressed.

Adaptor Proteins, Vesicular Transport↗
PubMed2006

The Petrolisthes galathinus complex: species boundaries based on color pattern, morphology and molecules, and evolutionary interrelationships between this complex and other Porcellanidae (Crustacea: Decapoda: Anomura).

While the amphi-American porcellanid crab Petrolistes galathinus has been traditionally viewed as a highly variable species containing several different color forms, we consider it to be a complex of at least 6 morphologically similar species with similar ecological requirements, but diagnosable through coloration. Here we surveyed sequence variation of the mitochondrial 16S rRNA gene, compared the morphology of adults and of the first larval stage (Zoea I), and explored shape variation of the sternal plate using geometric morphometric methods, to investigate boundaries among the species in the complex, and to confirm the validity of color and color pattern for distinguishing them. Sequences and larval morphological characters of other porcellanids were included to investigate the correspondence between genetic divergence and morphology of adults and larvae. The molecular and morphometric results support the validity of the species in the complex, and of color pattern for their distinction. The close relationship between the complex and the putative ancenstral porcellanid Parapetrolisthes tortugensis was indicated by the molecular and larval-morphology results. The adult morphology of this species is interpreted as a result of convergent evolution driven by a relatively rapid ecological adaptation to conditions in deeper waters. The nesting position in the phylogenetic trees of Petrocheles australiensis outside the Porcellanidae clade questions the monophyly of this family.

Animals↗
PubMed2000

Mechanism of the synergistic cytotoxicity between pentachlorophenol and copper-1,10-phenanthroline complex: the formation of a lipophilic ternary complex.

When non- or sub-toxic levels of pentachlorophenol (PCP) and bis-(1, 10-phenanthroline)cupric complex, Cu(II)(OP)(2), were combined, a remarkable synergistic toxicity was observed as indicated by growth inhibition and bacterial inactivation. Similar synergistic cytotoxic effects were observed with other polychlorinated phenols and other positively charged cupric complexes. The synergism observed for these chemicals and similar reactive pairs of chemicals was found to be due to the formation of lipophilic ternary complexes which facilitated copper transport into the bacterial cells. The formation of ternary complexes of similar lipophilic character could be of relevance as a general mechanism of toxicity.

Biological Transport↗
PubMed2003

Munc18-2/syntaxin3 complexes are spatially separated from syntaxin3-containing SNARE complexes.

Exocytosis of mast cell granules requires a vesicular- and plasma membrane-associated fusion machinery. We examined the distribution of SNARE membrane fusion and Munc18 accessory proteins in lipid rafts of RBL mast cells. SNAREs were found either excluded (syntaxin2), equally distributed between raft and non-raft fractions (syntaxin4, VAMP-8, VAMP-2), or selectively enriched in rafts (syntaxin3, SNAP-23). Syntaxin4-binding Munc18-3 was absent, whereas small amounts of the syntaxin3-interacting partner Munc18-2 consistently distributed into rafts. Cognate SNARE complexes of syntaxin3 with SNAP-23 and VAMP-8 were enriched in rafts, whereas Munc18-2/syntaxin3 complexes were excluded. This demonstrates a spatial separation between these two types of complexes and suggests that Munc18-2 acts in a step different from SNARE complex formation and fusion.

Animals↗
PubMed2003

Modeling the adsorption of free and heavy metal complex-bound EDTA onto red mud by a nonelectrostatic surface complexation model.

The adsorption of free and divalent heavy metal (copper, cadmium, and lead) complex-bound EDTA from metal-EDTA mixture solutions on a composite adsorbent having a heterogeneous surface, i.e., bauxite waste red mud, has been investigated and modeled with the aid of a nonelectrostatic surface complexation approach in respect to adsorbate concentration and pH dependency of EDTA adsorption. EDTA was selected as the modeling ligand in view of its wide usage as an anthropogenic chelating agent and its abundance in natural waters. The adsorption experiments were conducted for pure EDTA or metal-EDTA complexes alone, or in mixtures containing (EDTA+metal-EDTA). For all studied cases, the solid adsorbent phase concentrations of the adsorbed species were found by using the derived model equations with acceptable compatibility of experimental and theoretically generated adsorption isotherms. The model basically assumed two modes of metal bonding to the surface hydroxyls: ionic (outer-sphere) binding of the EDTA anion (H(2)Y(2-)) or anionic metal-EDTA complex (MY(2-)) to the cationic surface site ( approximately SOH(+)(2)), and outer-sphere binding of H(2)Y(2-) or MY(2-) to the neutral approximately SOH site, possibly via hydrogen-bonding. The model was useful for EDTA and metal-EDTA mixture solutions either at their natural pH of equilibration with the sorbent, or after pH elevation with NaOH titration up to pH<or=pzc of red mud. Thus adsorption of every single species (H(2)Y(2-) or MY(2-)) or of possible mixtures (H(2)Y(2-)+MY(2-)) at natural pH or after NaOH titration could be calculated by the use of simple quadratic equations at low metal loadings, once the initial concentrations of the corresponding species, i.e., [H(2)Y(2-)](0) or [MY(2-)](0), were known. The compatibility of theoretical and experimental data pairs of adsorbed species concentrations was verified by means of nonlinear regression analysis. The findings of this study, together with the previously developed (M(2+)+MY(2-)) mixtures adsorption model, can be further developed to serve environmental risk assessment concerning the expansion of a metal-organic (synthetic organic ligand or soil humic acids) contaminant plume with groundwater movement in soil basically consisting of hydrated oxide-type minerals.

Journal Article↗
PubMed2002

Crystal structure of the jacalin-T-antigen complex and a comparative study of lectin-T-antigen complexes.

Thomsen-Friedenreich antigen (Galbeta1-3GalNAc), generally known as T-antigen, is expressed in more than 85% of human carcinomas. Therefore, proteins which specifically bind T-antigen have potential diagnostic value. Jacalin, a lectin from jack fruit (Artocarpus integrifolia) seeds, is a tetramer of molecular mass 66kDa. It is one of the very few proteins which are known to bind T-antigen. The crystal structure of the jacalin-T-antigen complex has been determined at 1.62A resolution. The interactions of the disaccharide at the binding site are predominantly through the GalNAc moiety, with Gal interacting only through water molecules. They include a hydrogen bond between the anomeric oxygen of GalNAc and the pi electrons of an aromatic side-chain. Several intermolecular interactions involving the bound carbohydrate contribute to the stability of the crystal structure. The present structure, along with that of the Me-alpha-Gal complex, provides a reasonable qualitative explanation for the known affinities of jacalin to different carbohydrate ligands and a plausible model of the binding of the lectin to T-antigen O-linked to seryl or threonyl residues. Including the present one, the structures of five lectin-T-antigen complexes are available. GalNAc occupies the primary binding site in three of them, while Gal occupies the site in two. The choice appears to be related to the ability of the lectin to bind sialylated sugars. In either case, most of the lectin-disaccharide interactions are at the primary binding site. The conformation of T-antigen in the five complexes is nearly the same.

Antigens, Tumor-Associated, Carbohydrate↗
PubMed2003

The course of phosphorus in the reaction of N-acetyl-L-glutamate kinase, determined from the structures of crystalline complexes, including a complex with an AlF(4)(-) transition state mimic.

N-Acetyl-L-glutamate kinase (NAGK), the structural paradigm of the enzymes of the amino acid kinase family, catalyzes the phosphorylation of the gamma-COO(-) group of N-acetyl-L-glutamate (NAG) by ATP. We determine here the crystal structures of NAGK complexes with MgADP, NAG and the transition-state analog AlF(4)(-); with MgADP and NAG; and with ADP and SO(4)(2-). Comparison of these structures with that of the MgAMPPNP-NAG complex allows to delineate three successive steps during phosphoryl transfer: at the beginning, when the attacking and leaving O atoms and the P atom are imperfectly aligned and the distance between the attacking O atom and the P atom is 2.8A; midway, at the bipyramidal intermediate, with nearly perfect alignment and a distance of 2.3A; and, when the transfer is completed. The transfer occurs in line and is strongly associative, with Lys8 and Lys217 stabilizing the transition state and the leaving group, respectively, and with Lys61, in contrast with an earlier proposal, not being involved. Three water molecules found in all the complexes play, together with Asp162 and the Mg, crucial structural roles. Two glycine-rich loops (beta1-alphaA and beta2-alphaB) are also very important, moving in the different complexes in concert with the ligands, to which they are hydrogen-bonded, either locking them in place for reaction or stabilizing the transition state. The active site is too narrow to accommodate the substrates without compressing the reacting groups, and this compressive strain appears a crucial component of the catalytic mechanism of NAGK, and possibly of other enzymes of the amino acid kinase family such as carbamate kinase. Initial binding of the two substrates would require a different enzyme conformation with a wider active site, and the energy of substrate binding would be used to change the conformation of the active center, causing substrate strain towards the transition state.

Adenosine Diphosphate↗
PubMed1991

A quantitative evaluation of the effect of enzyme complexes on the glycolytic rate in vivo: mathematical modeling of the glycolytic complex.

The cellular distribution of free and bound glycolytic enzymes in vivo was estimated by means of a model based on previously determined association constants for individual binding interactions and in vivo protein concentrations. The calculations revealed that a significant proportion of the enzymes would be either associated with F-actin, or bound in binary enzyme-enzyme complexes in vivo. An analysis of the relative concentration, and relative activity, of F-actin-bound enzymes suggested that a complete glycolytic complex, composed of all enzymatic steps from phosphofructokinase (PFK) to lactate dehydrogenase (LDH) does not exist. This was indicated by a very low concentration of F-actin-associated phosphoglycerate kinase (PGK) and by a very low activity of F-actin bound aldolase and PGK; this model showed that aldolase and PGK would be absent from any F-actin bound complex. An analysis of soluble enzyme-enzyme associations indicated that formation of binary enzyme complexes may lead to an increased overall flux through glyceraldehyde 3-phosphate dehydrogenase and LDH, but would serve to decrease flux through PFK and aldolase. A 1.4-fold activation of PFK, which occurs when the soluble enzyme binds to F-actin, suggested that reversible binding of PFK to F-actin may represent a novel cellular mechanism for controlling glycolytic flux during periods of increased metabolic demand by controlling the key regulatory enzyme of glycolysis.

Actins↗
PubMed2000

Solution structure of the interacting domains of the Mad-Sin3 complex: implications for recruitment of a chromatin-modifying complex.

Gene-specific targeting of the Sin3 corepressor complex by DNA-bound repressors is an important mechanism of gene silencing in eukaryotes. The Sin3 corepressor specifically associates with a diverse group of transcriptional repressors, including members of the Mad family, that play crucial roles in development. The NMR structure of the complex formed by the PAH2 domain of mammalian Sin3A with the transrepression domain (SID) of human Mad1 reveals that both domains undergo mutual folding transitions upon complex formation generating an unusual left-handed four-helix bundle structure and an amphipathic alpha helix, respectively. The SID helix is wedged within a deep hydrophobic pocket defined by two PAH2 helices. Structure-function analyses of the Mad-Sin3 complex provide a basis for understanding the underlying mechanism(s) that lead to gene silencing.

Amino Acid Sequence↗
PubMed1999

Building a replisome from interacting pieces: sliding clamp complexed to a peptide from DNA polymerase and a polymerase editing complex.

We have solved the crystal structures of the bacteriophage RB69 sliding clamp, its complex with a peptide essential for DNA polymerase interactions, and the DNA polymerase complexed with primer-template DNA. The editing complex structure shows a partially melted duplex DNA exiting from the exonuclease domain at an unexpected angle and significant changes in the protein structure. The clamp complex shows the C-terminal 11 residues of polymerase bound in a hydrophobic pocket, and it allows docking of the editing and clamp structures together. The peptide binds to the sliding clamp at a position identical to that of a replication inhibitor peptide bound to PCNA, suggesting that the replication inhibitor protein p21CIP1 functions by competing with eukaryotic polymerases for the same binding pocket on the clamp.

Amino Acid Sequence↗
PubMed2000

Toward model complexes of Co-containing nitrile hydratases: synthesis, complete characterization and reactivity toward ligands such as CN- and NO of the first square planar CoIII complex with two different carboxamido nitrogens and two thiolato sulfur donors.

A [CoIII(N2S2)]NEt4 complex, with two carboxamido nitrogens and two alkylthiolato sulfurs, was prepared from N,N'-(2-thioacetylisobutyryl)-2-aminobenzylamine, and characterized. It crystallizes with a distorted square planar structure including two short Co-N bonds (approximately 1.882 A) and two short Co-S bonds (approximately 2.134 A). The ligand defines an 11-atom chelate, which may be Co ligands in the mean plane of Co-containing nitrile hydratase. The CoIII oxidation state, reversibly reduced at -1.13 V (vs. SCE) and irreversibly oxidized at +1.29 V (vs. SCE) in DMF, is stable over a 2 V potential range. From the temperature dependence of its magnetic susceptibility, cobalt(III) was found to be in an S = 1 triplet ground state, in agreement with the broad resonances observed in its 1H-NMR spectrum. Preliminary spectral studies showed that this complex does not interact with imidazole, H2O or HO-, but binds two CN anions or two NO molecules. The IR spectrum of the dinitrosyl complex exhibits two NO stretches at 1765 and 1820 cm(-1), in the range previously observed for dinitrosylated complexes derived from cobalt(I). This result suggests that, similarly to Fe NHases, Co NHases might readily bind NO.

Cobalt↗
PubMed2000

DNA targeted platinum complexes: synthesis, cytotoxicity and DNA interactions of cis-dichloroplatinum(II) complexes tethered to phenazine-1-carboxamides.

A series of intercalator-tethered platinum(II) complexes PtLCl2 have been prepared, where L are the diamine ligands N-[2-[(aminoethyl)amino]ethyl]-phenazine-1-carboxamide, N-[3-[(2-aminoethyl)amino]propyl]-phenazine-1-carboxamide, N-[4-[(2-aminoethyl)amino]butyl]-phenazine-1-carboxamide and N-[5-[(aminoethyl)amino]pentyl]-phenazine-1-carboxamide. Measurements of the time-course of unwinding of supercoiled pUC19 plasmid DNA by the phenazine complexes PtLCl2 reveal that the presence of the intercalator leads to enhanced rates of DNA platination when compared with the complex Pt(en)Cl2. The platinum(II) complexes where the polymethylene linker chain contains three, four or five carbon atoms are considerably more cytotoxic against murine P388/W than either cisplatin, Pt(en)Cl2, or the metal-free ligands themselves.

Animals↗
PubMed1997

Equilibrium and kinetic studies of iron(II) and iron(III) complexes of some alpha (N)-heterocyclic thiosemicarbazones. Reduction of the iron(III) complexes of 2-formylpyridine thiosemicarbazone and 2-acetylpyridine thiosemicarbazone by cellular thiol-like reducing agents.

alpha (N)-heterocyclic thiosemicarbazones have been shown to possess antitumor properties in mammalian cells through the inhibition of DNA synthesis; the ability to provide the inhibitory action is probably due to coordination of iron. This paper deals with equilibrium and kinetic studies involving 2-formylpyridine thiosemicarbazone (HFPT) and 2-acetylpyridine thiosemicarbazone (HAPT) coordinated to Fe(II) and Fe(III) cations in aqueous solution. The formation constants of all species present in equilibrium were determined. Kinetic measurements of the reduction of the Fe(III) complex of both ligands by thiolic reducing agents, that can act as structural models of cellular thiols, i.e., N-acetyl-L-cysteine (ACCIS) and dithiothreitol (DTT), were carried out. The experimental data lead to a rate law of the type v = k1[A] + k2[A] [B], where [A] represents the concentration of the complex and [B] that of the reducing agent, indicating the coexistence of two reaction pathways. One pathway depends only on the complex concentration and occurs even in the absence of the reducing agent, and the other involves both the complex and ACCIS or DTT.

DNA Replication↗