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  • 1. Beck, M.
    et al.
    Stiel, H.
    Leupold, D.
    Winter, B.
    Pop, D.
    Vogt, Ulrich
    Spitz, C.
    Evaluation of the energetic position of the lowest excited singlet state of beta-carotene by NEXAFS and photoemission spectroscopy2001Inngår i: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1506, nr 3, s. 260-267Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In carotenoids the lowest energetic optical transition belonging to the pi -electron system is forbidden by symmetry, therefore the energetic position of the S-1 (2(1)A(g)) level can hardly be assessed by optical spectroscopy. We introduce a novel experimental approach: For molecules with ir-electron systems the transition C1s --> 2p(pi*) from inner-atomic to the lowest unoccupied molecular orbital (LUMO) appears in X-ray absorption near edge spectra (NEXAFS) as an intense, sharp peak a few eV below the carbon K-edge. Whereas the peak position reflects the energy of the First excited singlet state in relation to the ionization potential of the molecule, intensity and width of the transition depend on hybridization and bonding partners of the selected atom. Complementary information can be obtained from ultraviolet photoelectron spectroscopy (UPS): At the low binding energy site of the spectrum a peak related to the highest occupied molecular orbital (HOMO) appears. We have measured NEXAFS and UPS of beta -carotene. Based on these measurements and quantum chemical calculations the HOMO and LUMO energies can be derived.

  • 2.
    Himo, Fahmi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    C-C bond formation and cleavage in radical enzymes, a theoretical perspective2005Inngår i: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1707, nr 1, s. 24-33Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    Quantum chemical methods are today a viable tool ill the Study of enzyme catalysis. The development of new density functional techniques and the enormous advancement in computer power have made it possible to accurately describe active sites of enzymes. This review gives a brief account of the methods and models used in this field. Three specific enzymes are discussed: pyruvate-formate lyase (PFL), spore photoproduct lyase (SPL), and benzylsuccinate synthase (BSS). What these enzymes have in common is that they use radical chemistry to catalyze C-C bond formation or cleavage reactions.

  • 3. Li, Yaqiong
    et al.
    Lin, Yuankui
    Garvey, Christopher J.
    Birch, Debra
    Corkery, Robert W.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Loughlin, Patrick C.
    Scheer, Hugo
    Willows, Robert D.
    Chen, Min
    Characterization of red-shifted phycobilisomes isolated from the chlorophyll f-containing cyanobacterium Halomicronema hongdechloris2016Inngår i: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1857, nr 1, s. 107-114Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Phycobilisomes are the main light-harvesting protein complexes in cyanobacteria and some algae. It is commonly accepted that these complexes only absorb green and orange light, complementing chlorophyll absorbance. Here, we present a new phycobilisome derived complex that consists only of allophycocyanin core subunits, having red-shifted absorption peaks of 653 and 712 nm. These red-shifted phycobiliprotein complexes were isolated from the chlorophyll f-containing cyanobacterium, Halomicronema hongdechloris, grown under monochromatic 730 nm-wavelength (far-red) light. The 3D model obtained from single particle analysis reveals a double disk assembly of 120-145 angstrom with two alpha/beta allophycocyanin trimers fitting into the two separated disks. They are significantly smaller than typical phycobilisomes formed from allophycocyanin subunits and core-membrane linker proteins, which fit well with a reduced distance between thylakoid membranes observed from cells grown under far-red light. Spectral analysis of the dissociated and denatured phycobiliprotein complexes grown under both these light conditions shows that the same bilin chromophore, phycocyanobilin, is exclusively used. Our findings show that red-shifted phycobilisomes are required for assisting efficient far-red light harvesting. Their discovery provides new insights into the molecular mechanisms of light harvesting under extreme conditions for photosynthesis, as well as the strategies involved in flexible chromatic acclimation to diverse light conditions.

  • 4. Mason, M. G.
    et al.
    Nicholls, P.
    Divne, Christina
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Hallberg, B. M.
    Henriksson, Gunnar
    KTH, Tidigare Institutioner                               , Pappers- och massateknik.
    Wilson, M. T.
    The heme domain of cellobiose oxidoreductase: a one-electron reducing system2003Inngår i: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1604, nr 1, s. 47-54Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Phanerochaete chrysosporium cellobiose oxidoreductase (CBOR) comprises two redox domains, one containing flavin adenine dinucleotide (FAD) and the other protoheme. It reduces both two-electron acceptors, including molecular oxygen, and one-electron acceptors, including transition metal complexes and cytochrome c. If the latter reacts with the flavin, the reduced heme b acts merely as a redox buffer, but if with the b heme, enzyme action involves a true electron transfer chain. Intact CBOR fully reduced with cellobiose, CBOR partially reduced by ascorbate, and isolated ascorbate-reduced heme domain, all transfer electrons at similar rates to cytochrome c. Reduction of cationic one-electron acceptors via the heme group supports an electron transfer chain model. Analogous reactions with natural one-electron acceptors can promote Fenton chemistry, which may explain evolutionary retention of the heme domain and the enzyme's unique character among secreted sugar dehydrogenases.

  • 5.
    Ojemyr, Linda Nasvik
    et al.
    Stockholm Univ, Dept Biochem & Biophys, Arrhenius Labs Nat Sci, S-10691 Stockholm, Sweden..
    Sanden, Tor
    Royal Inst Technol, Dept Appl Phys, Stockholm, Sweden..
    Widengren, Jerker
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvant- och biofotonik.
    Brzezinski, Peter
    Stockholm Univ, Dept Biochem & Biophys, Arrhenius Labs Nat Sci, S-10691 Stockholm, Sweden..
    Membrane-facilitated proton transfer to the surface of a membrane-spanning proton transporter2010Inngår i: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1797, s. 98-98Artikkel i tidsskrift (Annet vitenskapelig)
  • 6.
    Ojemyr, Linda
    et al.
    Stockholm Univ, Arrhenius Labs Nat Sci, Dept Biochem & Biophys, Stockholm, Sweden..
    Sanden, Tor
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Widengren, Jerker
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvant- och biofotonik.
    Brzezinski, Peter
    Stockholm Univ, Arrhenius Labs Nat Sci, Dept Biochem & Biophys, Stockholm, Sweden..
    Proton transfer along surfaces of membranes and membrane-proteins2008Inngår i: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1777, s. S94-S94Artikkel i tidsskrift (Annet vitenskapelig)
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