1,721,464 research outputs found
A functional heterologous electron-transfer protein complex: Desulfovibrio vulgaris flavodoxin covalently linked to spinach ferredoxin-NADP+ reductase
No full textThe water-soluble carbodiimide, N-ethyl-3-(3-dimethylaminopropyl)carbodiimide was found to readily promote formation of cross-links between spinach ferredoxin-NADP+ reductase and bacterial flavodoxins. The covalent complex between ferredoxin-NADP+ reductase and the Desulfovibrio vulgaris flavodoxin had a stoichiometry of 1 mol of flavodoxin per mole of the reductase, as assessed by denaturing electrophoresis, gel filtration and spectral analysis. The reductase moiety of the cross-linked complex gained the capacity to catalyze at a high rate the electron transfer from NADPH to cytochrome c without addition of free flavodoxin in the assay. The pH optimum for this activity was shifted to the alkaline region with respect to that for the noncovalent complex. FMN, the prosthetic group of flavodoxin, is required for electron transfer from the reductase FAD to cytochrome c. Structural studies carried out on the cross-linked complex allowed the identification of the peptide regions of the proteins involved in the interaction. The CNBr peptide 61-155 of the reductase was found cross-linked to the uncleaved flavodoxin, while the cross-linked region in flavodoxin appeared to be within the tryptic peptide 37-86. Treatment of flavodoxin with the carbodiimide in the presence of glycine ethyl ester brought about the modification of a few carboxyl groups and prevented its interaction with the reductase. It can be concluded that the bacterial flavodoxin binds to the reductase in a way similar to that of the physiological substrate ferredoxin (G. Zanetti, D. Morelli, S. Ronchi, A. Negri, A. Aliverti, and B. Curti, 1988, Biochemistry 27, 3753-3759). The cross-linked complex here described represents an useful model for studying electron transfer between the two flavoproteins
The crystal structure of FdxA, a 7Fe ferredoxin from Mycobacterium smegmatis
Full text linkMycobacterium smegmatis ferredoxin FdxA, which has an orthologue ferredoxin in Mycobacterium tuberculosis, FdxC, contains both one [3Fe-4S] and one [4Fe-4S] cluster. M. smegmatis FdxA has been shown to be a preferred ferredoxin substrate of FprA [F. Fischer, D. Raimondi, A. Aliverti, G. Zanetti, Mycobacterium tuberculosis FprA, a novel bacterial NADPH-ferredoxin reductase, Eur. J. Biochem. 269 (2002) 3005-3013], an adrenodoxin reductase-like flavoprotein of M. tuberculosis, suggesting that M. tuberculosis FdxC could be the physiological partner of the enzyme in providing reducing power to the cytochromes P450. We report here the crystal structure of FdxA at 1.6A resolution (R(factor) 16.5%, R(free) 20.2%). Besides providing an insight on protein architecture for this 106-residue ferredoxin, our crystallographic investigation highlights lability of the [4Fe-4S] center, which is shown to loose a Fe atom during crystal growth. Due to their high similarity (87% sequence identity), the structure here reported can be considered a valuable model for M. tuberculosis FdxC, thus representing a step forward in the study of the complex mycobacterial redox pathways
A three-domain iron-sulfur flavoprotein obtained through gene fusion of ferredoxin and ferredoxin-NADP+ reductase from spinach leaves
No full textFerredoxin and ferredoxin-NADP+ reductase are the two last partners of the photosynthetic electron-transfer chain, responsible for the final reduction of NADP+ to NADPH. Herein, we report the engineering and characterization of a novel protein molecule in which the electron-carrier protein (ferredoxin I) and the reductase (a flavoprotein) were covalently linked in a single polypeptide chain by gene fusion. The gene was obtained by joining the cDNAs encoding the respective proteins and subsequently by deleting the intervening sequence between them by site-directed mutagenesis. No extra amino acid residues were introduced between the C-terminus of ferredoxin I and the N-terminus of the flavoenzyme. The chimera was purified to homogeneity and characterized. The M(r) of the chimera apoprotein was 45,800 as determined by mass spectrometry, in agreement with the expected value of 45,846. Both flavin and iron-sulfur cluster were in 1:1 ratio with respect to the apoprotein. The chimera was found active as a diaphorase and, more interestingly, highly efficient as a cytochrome c reductase, without need for free ferredoxin addition in the assay medium. Several lines of evidence indicate that the ferredoxin and the reductase in the chimera assume a configuration quite similar to that in the dissociable physiological complex. Thus, the fusion protein could be a useful tool for studying the mechanism of protein-protein recognition and electron transfer in the ferredoxin-ferredoxin-NADP+ reductase system
Nuovi scenari di intervento pubblico nell’epoca degli squilibri globali
No full textL’articolo illustra la recente evoluzione del ruolo dello Stato, con un particolare riferimento agli interventi pubblici in relazione alla crisi finanziaria scoppiata nel 2008.
La prima parte analizza le responsabilità dei Governi nell’aver scatenato la crisi, ampliando l’offerta di credito. Si esamina innanzitutto la politica monetaria dei Paesi emergenti, in molti casi, come quello cinese, finalizzata alla difesa delle esportazioni, con l’effetto di generare imponenti flussi di risparmio destinati ai Paesi sviluppati. Si discute poi il ruolo delle politiche dei Paesi avanzati, e in particolare delle politiche monetaria e abitativa statunitensi, e della deregolamentazione finanziaria.
La seconda parte tratta degli aspetti critici dell’intervento pubblico in risposta alla crisi, evidenziando l’impatto negativo di alcune politiche, in particolare di tipo contabile, che hanno contribuito ad esacerbare la tendenza al dirottamento di capitali verso impieghi inefficientemente poco rischiosi, con la conseguenza di rallentare la crescita economica.
Infine, con l’ausilio di un semplice modello di teoria dei giochi, si evidenzia la necessità di una politica regolatoria coordinata fra i diversi Paesi, finalizzata a prevenire nuovi fenomeni di cris
Relazioni verticali e organizzazione d’impresa: nuove tematiche sul fronte dell’oligopolio
No full textIl saggio analizza lo sviluppo recente dei modelli di oligopolio in riferimento alle strutture verticali, caratterizzati, cioè, da una filiera di produzione organizzata in diversi stadi successivi
New Forms of Government Intervention in the Era of Global Imbalances
No full textThe paper illustrates how the Government role has recently evolved, specifically focusing on the 2008 financial crisis.
First, we analyze the Government responsibilities in triggering the crisis, by bloating the supply of credit. We discuss emerging countries’ expansionary monetary policy, in many cases aimed at defending their export, thereby directing huge savings flows towards developed countries. We then expound the role of the US housing and monetary policies, as well as other countries’ policies, particularly regarding financial deregulation. Second, we deal with some critical aspects of Governments’ intervention in the aftermath of the crisis. We show the negative impact of a number of policies, particularly in the accounting field, which contributed to exacerbating the tendency to an inefficient allocation of the available capital, where an excessive weight has been placed on low-risk assets, resulting in a slowdown of economic growth.
Finally, we use a simple game theoretic model to emphasize the need for an internationally coordinated financial regulation policy
“Distributed quantitative evaluation of 3D patient specific arterial models”
No full textIn this paper we describe a new system for the 3D reconstruction and distribution on the net of models for vessels structures. The system is specifically designed to support measurements of medical interest. We describe 2D and 3D segmentation methods implemented and the procedure used to build interactive VRML97 models. The experimental section presents a comparison between segmentation methods, and a first application to surgical planning for endovascular repair of Abdominal Aortic Aneurysms
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