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1984 (1)
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1Author    ErichF. Elstner, Claus Stoffer, Adelheid HeupelRequires cookie*
 Title    Determination of Superoxide Free Radical Ion and Hydrogen Peroxide as Products of Photosynthetic Oxygen Reduction  
 Abstract    Formation of Nitrite from Hydroxylamine in the presence of illuminated chloroplast lamellae is inhibited by superoxide dismutase but not by catalase, indicating that the superoxide free radical ion and not H20 2 is responsible for the oxidation of hydroxylamine. Decarboxylation of a-keto acids on the other hand is strongly inhibited by catalase but only slightly by superoxide dismutase. Light-dependent hydroxylamine oxidation and decarboxylation of a-keto acids can be used, there­ for, as specific and sensitive probes for the determination of either the superoxide free radical ion or hydrogen peroxide, respectively. Photosynthetic oxygen reduction in the presence of ferredoxin, (monitored by the above method) yields both H20 2 and 0 2 ". The addition of an oxygen reducing factor (ORF, solubilized by heat — treatment of washed chloroplast lamellae) instead of ferredoxin, however, stimulates only the production of H20 2 , while 0 2'~ — formation is not observed. The cooperation of ferredoxin and ORF during photosynthetic oxygen reduction by chloroplast lamellae apparently produces H20 2 not only by dismutation of 0 2'~, but also by a separate mechanism involving ORF. yields only in the formation of H20 2 . The coopera­ tion of Fd and ORF in photosynthetic oxygen re­ duction provides a system which is able to produce HoOo and 0 2~ simultanuously. During photosyn­ thetic oxygen reduction, H 20 2 is not only the product of the dismutation of the superoxide free radical ion according to Eqn (1) 0 2'-+ Oo ~ + 2 H +-> H2Oo + 0 2 (1) but is separately formed by a mechanism which includes the function of ORF. Material and Methods Ferredoxin was isolated from spinach leaves9 and SOD from dried green peas 10, 5. Chloroplasts were isolated either from spinach 11 or from sugar beet leaves12' 7. ORF was prepared from isolated chloroplast lamellae 7 from either spinach or sugar beet leaves. Photosynthetic decarboxylation of [l-14C]gly-oxylate13, NADP-reduction13 and nitrite-forma-tion 14 from hydroxylamine were measured as de­ scribed. Sugar beet leaves (greenhouse cultures) were a gift from the Kleinwanzlebener Saatzucht AG, Einbeck/Hann. [1-14C] sodium glyoxylate was obtained from the Radiochemical Center, Amersham. Catalase was purchased from Boehringer, Mannheim. 
  Reference    (Z. Naturforsch. 30c, 53 [1975]; received October 25 1974) 
  Published    1975 
  Keywords    Chloroplasts, Oxygen Reduction, Hydroxylamine Oxidation, Superoxide Free Radical Ion 
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 TEI-XML for    default:Reihe_C/30/ZNC-1975-30c-0053.pdf 
 Identifier    ZNC-1975-30c-0053 
 Volume    30 
2Author    E. F. Elstner, D. From, M. EyerRequires cookie*
 Title    Analysis of Different Mechanisms of Photosynthetic Oxygen Reduction  
 Abstract    Three mechanisms of oxygen reduction by chloroplast lamellae in the presence of autoxidizable electron acceptors can be differentiated by product analyis in the presence or absence of either dibromothymoquinone (DBMIB) or superoxide dismutase (SOD) : 1) H20 2 is the product of two-electron oxygen reduction by 2,3-dimethyl-5,6-methylenedioxy-p-benzoquinone, involving only photosystem II. This reaction is not inhibited by either DBMIB or SOD. 2) Superoxide anion, and H20 2 as the product of its dismutation, are products of monovalent oxygen reduction following autoxidation of certain low potential electron acceptors (herbicides) of photosystem I. These reactions are not inhibited by SOD but are blocked by DBMIB. 3) H20 2 is the product of and "apparent" two-electron photoreduction of oxygen, mediated by certain o-diphenols (caffeic acid). These reactions are inhibited by both DBMIB and SOD in­ dicating the involvement of photosystem I and of 0 2-as an intermediate in the H20 2 producing reaction. 
  Reference    Z. Naturforsch. 33c, 276 (1978); received February 6 1978 
  Published    1978 
  Keywords    Oxygen Reduction, Photosynthetic Electron Transport, Superoxide Anion, Peroxide Formation, Chloroplasts 
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 TEI-XML for    default:Reihe_C/33/ZNC-1978-33c-0276.pdf 
 Identifier    ZNC-1978-33c-0276 
 Volume    33 
3Author    DietrichW. Abner, Rudolf Holze, Peter SchmittingerRequires cookie*
 Title    Impedance of an Oxygen Reducing Gas-Diffusion Electrode  
 Abstract    The impedance of teflon bonded electrodes was measured in the frequency domain. These electrodes based on activated carbon as electrocatalyst were developed for fuel cell applications. When feeding the electrode with air or oxygen the impedance spectra could be explained by two Nernst diffusion processes and a small charge transfer process. Two methods for separating the measured impedance into partial impedances related to differ­ ent steps of the electrode reaction are presented. A least square fit procedure is described which has been applied successfully to the impedance analysis of porous electrodes. List o f symbols Symbol Dimension A diffusion factor VT c concentration of diffusing species at electrode surface mol/dm3 cD double layer capacity mF/cm2 d diffusion layer thickness ^m D diffusion coefficient cm2/s f frequency Hz F Faraday constant As/mol i current density mA/cm2 Im(Z) imaginary part of the complex impedance Z Q or Q • cm j imaginary quantity V~1 -R resistance Q or Q ■cm T > ^ o .i m p sum of the resistive parts of the Faradaic impedance Q or Q • cm' R o ,i/ s slope of the potential vs. current density curve at the point of the im­ pedance measurement Q or Q ■cm' R -d o diffusion resistance Q or Q ■cm' R d charge transfer resistance (equiva­ lent to Rct) Q or Q ■cm Re(Z) real part of the complex impedance 2 Q ox Q ■cm Rei electrolyte resistance Q z d diffusion impedance Q or Q ■cm ZD charge transfer impedance (equivalent to Zct) f i o r f l ■ cm' z, residual impedance ß o r ß -cm' Y electrochemical equivalent mol/As CO angular frequency (a> = 2 jtF) Hz * Sonderdruckanforderungen an Privatdozent Dr. Diet-rich Wabner, Arbeitsgruppe Angewandte Elek­ trochemie im 
  Reference    Z. Naturforsch. 39b, 157 (1984); eingegangen am 24. August 1983 
  Published    1984 
  Keywords    Nernst-Impedance, Fuel Cell Electrode, Oxygen Reduction, Gas Diffusion Electrode, Teflon Bonded Electrode 
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 TEI-XML for    default:Reihe_B/39/ZNB-1984-39b-0157.pdf 
 Identifier    ZNB-1984-39b-0157 
 Volume    39