72 research outputs found
Quinolinate synthase, an iron-sulfur enzyme in NAD biosynthesis
International audienceNicotinamide adenine dinucleotide (NAD) plays a crucial role as a cofactor in numerous essential redox biological reactions. NAD derives from quinolinic acid which is synthesized in E. coli from L-aspartate and dihydroxyacetone phosphate (DHAP) as the result of the concerted action of two enzymes, L-aspartate oxidase (NadB) and quinolinate synthetase (NadA). We report here the characterization of NadA protein from E. coli. When anaerobically purified, the isolated soluble protein contains 3-3.5 iron and 3-3.5 sulfide/ polypeptide chain. Mössbauer spectra of the 57Fe-protein revealed that the majority of the iron is in the form of a (4Fe-4S)2+ cluster. An enzymatic assay for quinolinate synthetase activity was set up and allowed to demonstrate that the cluster is absolutely required for NadA activity. Exposure to air leads to degradation of the cluster and inactivate enzyme
Spectroscopic and nanoscale characterization of blue-coloured smithsonite (ZnCO3) from Lavrion historical mines (Greece)
Spectroscopic and microscopic (particularly HRTEM) techniques were used to investigate
the origin of the colour of natural blue Zn-carbonate (smithsonite). Blue smithsonite is
rich in copper, but substitution of zinc cations by copper cations, as proposed in the past
for the origin of the colour, is questionable considering the absence of anhydrous divalent
copper carbonates in nature. In this work, optical microscopy, SEM-EDS, XRD and laser
micro-Raman could not resolve distinct phases either than Zn-carbonate, while NIR spectra
excluded known chromophore Cu-hydroxycarbonate minerals. HRTEM studies however
could clearly resolve nano-sized (3-7 nm) Cu-rich inclusions (specifically Si/Ca/Cu/As-rich
inclusions of at least one phase), which are organised in bands with no topotaxial relation
to bulk smithsonite. Electron-beam sensitivity of the samples, even at low electron current
densities, did not allow the exact identification of the inclusions. However, it can be safely
suggested, for the first time in the literature, that they are the cause of the blue colour in
smithsonite
A general synthetic route for the preparation of high-spin molecules: Replacement of bridging hydroxo ligands in molecular clusters by end-on azido ligands
Abstract A general method of increasing the ground-state total spin value of a polynuclear 3d-metal complex is illustrated through selected examples from cobalt(II) and nickel(II) cluster chemistry that involves the dianion of the gem-diol form of di-2-pyridyl ketone and carboxylate ions as organic ligands. The approach is based on the replacement of hydroxo bridges, that most often propagate antiferromagnetic exchange interactions, by the end-on azido ligand, which is a ferromagnetic coupler
Iron-Sulfur Cluster Biosynthesis: characterization of Escherichia coli CyaY as an iron donor for the assembly of (2Fe-2S) clusters in the scaffold IscU
International audienc
- …