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'Electron Transport' in keywords Facet   Publication Year 1989  [X]
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1Author    JaspreetA. Rora, P. V. SaneRequires cookie*
 Title    Histidyl Residues Mediate Electron Transport in Plant Mitochondria  
 Abstract    Plant The effect of chemical modification of histidyl residues using diethyl pyrocarbonate (D EP) on plant mitochondrial electron transport was studied. Mitochondrial membranes from potato tubers were isolated and electron flow from N A D H to oxygen, NADH to ferricyanide and ascorbate to oxygen were monitored in pro», nee and/or absence of DEP. Measurements were made at various concentrations of DEP and at different pHs either by using an oxygen electrode or spectro-photometrically. The results show that DEP inhibits flow of electrons from NADH to oxygen, however partial electron transport from N A D H to ferricyanide and ascorbate to oxygen was unaffected. Maximum inhibition was observed at pH 6.5. The time course of the DEP action revealed a biphasic nature of inhibition. Effects on the levels of reduction of cytochromes b and c by DEP during electron transport indicated that histidyl residues may be present before or at cytochrome b , which are being modified. 
  Reference    Z. Naturforsch. 44c, 537 (1989); received April 7 1989 D edicated to 
  Published    1989 
  Keywords    Mitochondria, Histidine Modification, Electron Transport, Spectral Studies 
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 TEI-XML for    default:Reihe_C/44/ZNC-1989-44c-0537.pdf 
 Identifier    ZNC-1989-44c-0537 
 Volume    44 
2Author    U. H. Eber, J. Viil, S. Neimanis, T. Mimura, K.-J DietzRequires cookie*
 Title    Photoinhibitory Damage to Chloroplasts under Phosphate Deficiency and Alleviation of Deficiency and Damage by Photorespiratory Reactions  
 Abstract    D edicated to P rofessor A chim Trebst on the occasion o f his 60th birthday Effects of Pi deficiency on photosynthesis ot isolated spinach chloroplasts were examined. The following observations were made: (1) Chloroplasts isolated in Pi-free media evolved oxygen in the light in the absence of added Pi until acid-extractable P, in the chloroplasts had decreased to 1 to 2.5 m M . This Pj was unavailable for photophosphorylation as shown by the inability of the chloroplasts to respond by oxygen evolution to the addition of PGA. In the state of Prdeficiency, stromal ATP to A DP ratios were in the light close to or below ratios observed in the dark. In the presence of 2 mM PGA, addition of 20 (j.m Pi was insufficient to increase ATP to ADP ratios, but sufficient for appreciable oxygen evolution. (2) More Pi was available for oxygen evolution of phosphate-deficient chloroplasts at low levels of C 0 2 than at high levels. This was due mainly to the suppression of oxygenation of RuBP by high C 0 2 levels which prevented formation of phosphoglycolate and the subsequent release of Pi into the chloroplast stroma. (3) More oxygen was produced by phosphate-deficient chloroplasts at a low light intensity than at a high light intensity. This was due to increased availability of endogenous Pi under low light and to photoinhibition of the chloroplasts by high light. The main product of photosynthesis of phosphate-deficient chloroplasts in the presence of a high bicarbonate concentration was starch, and the main soluble product was PGA. (4) After phosphate-deficient chloroplasts had ceased to evolve oxygen in the light, they be­ came photosensitive. Part of the loss of the capacity for oxygen evolution is attributed to leakage of PGA, but the main reason for loss of function is photoinactivation of electron transport. Both photosystems of the electron transport chain were damaged by light. (5) Protection against photoinactivation was provided by coupled electron transport. Photo­ inactivation of phosphate-deficient chloroplasts was less extensive in the presence of low C 0 2 concentrations which permitted oxygenation of RuBP than at high CO: concentrations. Electron transport to C 0 2 and other physiological electron acceptors and to the herbicide methylviologen was also protective. However, electron transport to oxygen in the Mehler reaction failed to provide appreciable protection against high light intensities, because oxygen reduction is slow and reactive oxygen species produced in the light contribute to photoinactivation. 
  Reference    Z. Naturforsch. 44c, 524 (1989); received February 3 1989 
  Published    1989 
  Keywords    Photosynthesis, Photoinhibition, Photorespiration, Electron Transport, Phosphate Deficiency, Phosphate Homeostasis 
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 TEI-XML for    default:Reihe_C/44/ZNC-1989-44c-0524.pdf 
 Identifier    ZNC-1989-44c-0524 
 Volume    44