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Phycocyanobilin:ferredoxin
oxidoreductase (PcyA) |
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Phycocyanobilin:ferredoxin
oxidoreductase (PcyA) , is an enzyme of a new class of ferredoxin-dependent
bilin reductases, which are radical enzymes that require neither cofactors nor
metals and act by reducing the vinyl groups of the biliverdin (BV). During this
reaction four electrons are transferred from ferredoxin to produce
phycocyanobilin. High-field EPR single crystal studies of PcyA yielded precise
information about the geometry of the g-tensor in the
protein. We are currently investigating the topology of the reactive
intermediates as well as the thermodynamic aspects of the reduction reaction
such as the electron-proton transfer barriers or the influence of the conformational
changes on the proton transfer using advanced quantum chemistry computation
within the ONIOM scheme. In collaboration with Prof. Wesolowski from the
University of Geneva, the quantification of the subtle changes in the electron
density surrounding the BV by monitoring the variation induced by the mutation
of some of the relevant amino-acids in the surrounding on the g matrix values
and orientation, is performed with the recently implemented embedded frozen
density formalism of Warshal and Wesolowski.
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Mechanism of Cu(II) transport through the PLM membranes |
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The
understanding of the exact mechanism of Cu(II) transport through the
existing PLM membranes containing the mixture of azacrown ether and
fatty acid as a carrier is the main goal of this project. In the given
PLM system both azacrown ether and fatty acid could serve as a carrier,
since both are known to complex Cu(II) in bulk and both modes of copper
complexation and transport in the PLM membrane should be carefully
verified. EPR and EXAFS studies on such complexes are currently in
progress.
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High-Field 31P ENDOR of the Mn coordination to nucleotides and nucleic acids
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Managanese-phosphate coordination is important in
many natural systems, and especially in systems containing ADP (adenosine diphosphate)
and ATP (adenosine triphosphate). Poor resolution of the CW techniques in
probing the bonding of metal ions to nucleotides and nucleic acids can be
overcome using 31P pulsed electron-nuclear double resonance (ENDOR)
techniques, especially applied at higher magnetic fields. We are currently investigating
the coordination environment of the managanese ion in enzymatic systems
containing phosphate groups using a sensitive pulsed Mims and Davies pulse
sequences at 130 GHz. Preliminary data on Mn-nucleotides complexes show that
this techniques provides axcellent resolution and it can be applied sucesfully
to the very small sample volumes of biological samples
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Quantum Chemical investigation of the secondary metal - arene interactions in the transition metal dimers ArMMAr (Ar = Terphenyl; M = Cr, Fe or Co)
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Understanding
the nature of the feeble interaction between the transition metal and π systems is of crucial interest in the context
of the recent development of the multiple bonding between transition metals. In
collaboration with Laura Gagliardi's group from University of
Geneva we are working towards understanding of the large differences between
the pi-metal interactions in the
transition-metal dimers ArMMAr (Ar = Terphenyl; M = Cr, Fe, or Co). These
differences have profound implications for the Cr−Cr quintuple bonding. Our
theoretical studies indicate that in the Cr−Cr species the Cr−arene
interaction is quite feeble and does not affect the quintuple bonding, however
in the analogous Fe and Co species strong η6-arene interactions
preclude higher order metal−metal bond.
metry.
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