196,095 research outputs found
The elusive role played by the side chain of Lys249 of Plasmodium falciparum ferredoxin-NADP+ reductase in NADPH/NADH selectivity
No full textPlasmodium falciparum, the causative agent of tropical malaria, possesses plant-type ferredoxin-NADP+ reductase (PfFNR) and ferredoxin (PfFd), which have been proposed as targets for novel antimalarial drugs (1). The catalytic mechanism of PfFNR is under study in order to provide the bases for the design of effective enzyme inhibitors (2). Although PfFNR is quite specific for NADPH, no structural evidence was obtained for protein positive groups interacting with the 2’-phosphate of this substrate (3). We have found that change of Lys249 to Ala decreased the kcat/Km for NADPH by a factor of 10, without affecting the activity of the enzyme with NADH. In addition, PfFNR-K249A displayed an affinity for NADP+ 8-fold lower than those of the wild-type enzyme. We conclude that the side-chain of Lys249 actually interacts with the 2’-phosphate of NADPH during the catalytic cycle, and that it is part of a region flexible enough to adopt in the crystal form of the protein a conformation where such interaction is severed 1. Seeber, F., et al. (2005) Curr. Pharm. Des. 11, 3159-3172.
2. Crobu, D., et al. (2009) Biochemistry 48, 9525-9533.
3. Milani, M., et al. (2007) J. Mol. Biol. 367, 501-513
Preliminary characterization of the water soluble complex Rh/Human Serum Albumine, an active catalyst for olefin hydroformylation
No full textToF-SIMS of polyphosphate glasses
No full textThe increasing interest in phosphate glasses is due to the fact that they are considered to be bioactive functional materials in applications such as hard and soft tissue engineering and also that they possess interesting optical properties. These include
low dispersion, high refractive index and high transparency for ultraviolet light. They have also been found to be responsible for the good anti-wear properties of phosphorus-based engine-oil additives. More recently, the low processing temperature of
zinc and iron phosphates, as well as their chemical durability, has opened the possibility for new applications, such as the immobilization of nuclear wastes. Understanding the surface chemistry of such glasses turns out to be a key step for inferring
their underlying mechanisms of action. In this work, zinc phosphate and iron phosphate glasses of different chain lengths were synthesized and characterized by means of time-of-flight secondary ion mass spectroscopy (ToF-SIMS). ToF-SIMS was
able to successfully differentiate between the samples of different composition. A characteristic pattern of phosphate fragments was observed in the negative-mode ToF-SIMS spectra. The most intense peaks could be assigned to the phosphate
fragments PO, PO2, PO3 and PO4. Toward higher masses, fragments containing up to four phosphorus atoms with a periodicity of PO2 were observed: FePO3, ZnPO3, FePO4, ZnPO4, FeP2O6, ZnP2O6, FeP2O7, ZnP2O7; FeP3O8, ZnP3O8,FeP3O9and ZnP3O9. This pattern characterizes the spectra of all the glasses under investigation. For the first time, a method is proposed that allows the discrimination between polyphosphates of different chain lengths, by comparing the intensities of the relevant ToF-SIMS peaks
Studies of interaction between Rh(I) and Human Serum Albumin in a "nanostructured biocatalyst" active in the hydroformylation reaction
No full textThe interaction between Rh(CO)2(acac = acetylacetonate ion) and human serum albumin (HSA) in a hydrosoluble nanostructured
biocatalyst active in homogeneous hydroformylation was characterised by means of matrix assisted laser desorption ionization timeof-
flight mass spectrometry (MALDI-TOFMS), high performance liquid chromatography mass spectrometry (HPLC-MS) and scanning
electron microscopy (SEM). MALDI-TOFMS substantiates that the biocatalyst consists of a tetrameric structure of HSA that could
bind up to 89 RhðCOÞþ
2 units. A comparison between samples of pure HSA and the biocatalyst, both tryptic digested, showed a significant
change in the tertiary structure of the protein in the HSA/Rh adduct, probably ascribable to the interaction of Rh(I) ions with
sulphur atoms in the HSA moiety. SEM observations confirmed an evident denaturation of the protein and an outstanding correspondence
between the surface distribution of Rh and S atoms; this is indirect evidence that the metal ion interacts strongly mainly with the
sulphur atoms. Furthermore, an excellent agreement between calculated and measured (SEM) S/Rh elemental mean ratio was observed.
Finally, an electrostatic interaction between Rh(I) and sulphur atoms was ruled out by sodium dodecyl sulfate polyacrylamide gel electrophoresis
(SDS–PAGE) findings
Chain-Length-Identification Strategy in Zinc Polyphosphate Glasses by Means of XPS and ToF-SIMS
No full textThe surface chemistry of amorphous zinc polyphosphates of different compositions (ranging from zinc metaphosphate to zinc orthophosphate) has been investigated by means of X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary-ion mass spectroscopy (ToF-SIMS). The identification of the chain length of zinc polyphosphates by XPS could be achieved on the basis of the integrated intensity ratio of the bridging (P-O-P) and non-bridging (P=O and P-O-M) oxygen peaks used for fitting the oxygen 1s signal, the shift of the P 2p3/2 signal towards lower binding energies, and of the modified Auger parameter towards higher values as the zinc content increases. The discrimination of the polyphosphate chain lengths could be also achieved by ToF-SIMS, by comparing the intensities of selected characteristic phosphate fragments. Both techniques appear to be suitable for the investigation of polyphosphate glasses in applications such as tribology, where there is a need to identify the chain length present in the outermost monolayer of the film.
Fourier-transform infrared (FT-IR) spectroscopy was used in order to characterize the bulk compounds. The FT-IR studies showed that long-chain structures linked through P-O-P bonds predominate in the metaphosphate composition, while upon increasing the Zn content, the chains become shorter, ultimately being replaced by PO4 monomers in the orthophosphate composition
Ebselen : an antimalarial compound active against ferredoxin-NADP+ reductase of Plasmodium falciparum
No full textEbselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one)is a seleno-organic compound that has been extensively studied as an anti-inflammatory drug. It reacts with thiol groups forming selenylsulphide bonds and it has been reported to inhibit a variety of enzymes involved in different processes1. Moreover, ebselen has been shown possesse an antimalarial activity in vitro against P. falciparum strains in the asexual stages. Since this compounds displayed no cytotoxic effects on human epatocyte, it is of interest for the design of antimalarial drugs2. The effect of ebselen on ferredoxin-NADP+ reductase of Plasmodium falciparum (PfFNR), an enzyme located in the apicoplast of the parasite3, has been investigated. Ebselen was found to slowly and irreversibly inhibit PfFNR targeting one or more Cys residue of the enzyme. Spectrofluorimetric studies pointed out that ebselen promotes the release of prosthetic group FAD. PfFNR was found to be particularly sensitive to inactivation in comparison to similanr flavoenzymes. The compound is 9-fold less active against the omologue FNR from spinach leaf, while Mycobacterium tuberculosis FprA, a ferredoxin-reductase structurally unrelated to plant type FNRs, turned out to be completely insensitive to this inhibitor, These preliminary data suggest that PfFNR could be a potential target of the antiplasmodial activity of ebselen.1. Schewe T. (1995) Gen. Pharmac. 26 (6): 1153-1169 2. Huter A. M. et al. (1989) Parasitol Res. 75 (5): 353-60 3. Seeber F. et al. (2005) Curr. Pharm. Des. 11, 3159-317
Effect of Chain-Length and Countersurface on the Tribochemistry of Bulk Zinc Polyphosphate Glasses
No full textZinc polyphosphate glasses are considered to be chiefly responsible for the anti-wear efficiency of ZnDTP tribofilms. In this work, the tribochemical properties of amorphous bulk zinc polyphosphates of different chain lengths (ranging from zinc metaphosphate to zinc pyrophosphate) have been investigated. Tribological tests on bulk polyphosphate discs have been carried out using steel and quartz balls as counter-surfaces in a poly-α-olefin (PAO) bath at room temperature. The composition in the wear track and on the contact region of the balls has been monitored by small-area and imaging X-ray photoelectron spectroscopy (i-XPS). The XPS analysis revealed that the composition of short-chain-length polyphosphates remained unchanged following tribological stress. Long-chain-length polyphosphates are depolymerized in the wear track as a consequence of a tribochemical reaction. By comparing the results obtained using quartz and steel balls, it could be observed that while the reaction of iron oxide with the polyphosphates certainly plays a role in the depolymerization of the samples under sliding conditions, pressure and shear stress alone and also in the presence of water or oil-oxidized species are able to depolymerize the glass when an inert material is used as counterpart; the composition of the wear track, in this case, is dependent on the applied load. All samples were able to form an adhesive, glassy transfer film on both steel and quartz balls, but the short-chain-length polyphosphates showed a lower friction coefficient and wear coefficient. The results suggest a third-body mechanism with the polyphosphates acting as a solid lubricant. Differences in tribological behavior of the different-chain-length polyphosphates are attributable to their mechanical and rheological properties
ToF-SIMS of Polyphosphate Glasses
No full textPhosphate glasses have been investigated in detail, due to their interesting optical properties: low dispersion, high refractive index and high transparency for ultraviolet light. More recently, the low processing temperature of zinc and iron phosphates as well as their chemical durability opened the possibility for new applications, such as immobilization of nuclear wastes and biomechanical properties. Polyphosphate glasses have also been investigated for their anti-wear properties, since almost all common engine oil additives contain phosphorus and are able, under sliding conditions, to react on steel surfaces to form a protective tribofilm mainly constituted of glassy polyphosphates The characterization of the surface chemistry of such glasses turns out to be a key step for understanding their mechanism of action.
In this work zinc and iron phosphate glasses of different chain length were synthesized and characterized by means of ToF-SIMS. ToF-SIMS was able to successfully differentiate between the samples of different composition
Ferredoxin–NADP+ reductases of Apicomplexa: unique properties of protozoan plant–type enzymes
No full textPlant-type ferredoxin-NADP+ reductases (FNRs) are a family of flavin-dependent dehydrogenases/electron transferases ubiquitous in plant plastids, cyanobacteria and some eubacteria (1). Recently, FNRs have been identified in the apicoplast of apicomplexan parasites, which includes the causative agents of malaria and toxoplasmosis. FNRs from Toxoplasma gondii (TgFNR) and Plasmodium falciparum (PfFNR) have been cloned and characterized (2, 3). Whereas TgFNR failed to yield crystals suitable for X-ray analysis, the crystal structure of PfFNR has been determined (3). Compared to FNRs from other sources, PfFNR displays a significantly lower catalytic efficiency and poorer NADH/NADPH selectivity (3). These features of PfFNR have been interpreted on the basis of the peculiar structure of its NADP(H)-binding site. Furthermore, PfFNR undergoes an unprecedented NADP-triggered, redox-dependent homodimerization process leading to enzyme inactivation, which could represent a physiologic mechanism of enzyme regulation. PfFNR has been shown to be involved in the biosynthesis of isoprenoid precursors (4), which is the site of action of known antiplasmodial compounds. On this basis, apicomplexan FNRs have been proposed as a possible new target for novel antiparasitic drugs (2).
References
1. Aliverti, A., Pandini, V., Pennati, A., de Rosa, M., and Zanetti, G., Arch. Biochem. Biophys., 474, 283-291 (2008).
2. Seeber, F., Aliverti, A., and Zanetti, G., Curr. Farm. Des., 11, 3159-7312 (2005).
3. Milani, M., Balconi, E., Aliverti, A., Mastrangelo, E., Seeber, F., Bolognesi, M., and Zanetti, G., J. Mol. Biol., 367, 501-513 (2007).
4. Röhrich, R.C., et al., FEBS Lett., 579, 6433–6438 (2005)
Well differentiated mesothelioma of the right uterosacral ligament: A case report
No full textWell differentiated papillary mesothelioma is a rare type of mesothelioma of the peritoneum, mainly found in women of reproductive age, and often misdiagnosed as an ovarian mass. We report a case of a 46-years old woman, with a clinical suspect of an adnexal mass, in whom the peritoneal mesothelioma was diagnosed and successfully removed at laparoscop
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