Inhibition of exogenous NADH oxidation in plant mitochondria by chlorotetracycline in the presence of calcium ions |
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Authors: | Ian M. Møller John M. Palmer Sally P. Johnston |
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Affiliation: | 1. Department of Plant Physiology, University of Lund, Box 7007, S-220 07 Lund Sweden;2. Department of Pure and Applied Biology, Imperial College of Science and Technology, Prince Consort Road, London SW7 2BB U.K. |
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Abstract: | Chlorotetracycline inhibits the uncoupled oxidation of exogenous NADH by Jerusalem artichoke (Helianthus tuberosus L.) mitochondria extensively (over 80%) and rapidly (inhibition complete in 10 s) in the presence of added Ca2+. Half-maximal inhibition is observed at 15 μM chlorotetracycline in the presence of 2 mM Ca2+. The oxidation of succinate is only affected marginally by chlorotetracycline plus Ca2+. The inhibition of NADH oxidation and the fluorescence of CTC are well correlated. Mn2+ is the only other cation which shows an (increased) inhibition in the presence of chlorotetracycline. The inhibition by Ca2+ and chlorotetracycline disappears at acid pH, and the pH optimum in their presence is 6.4. The inhibition caused by other lipid-soluble Ca2+-chelators is not reversible or is enhanced by the addition of excess Ca2+. In contrast, inhibition caused by relatively water-soluble chelators is completely reversed by added Ca2+. It is suggested that a neutral 1:2 complex is formed between Ca2+ and chlorotetracycline which can substitute for Ca2+ bound at sites in the lipophilic phase of the inner mitochondrial membrane, which are essential for the activity of the external NADH dehydrogenase. |
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Keywords: | NADH oxidation Chlorotetracycline (Plant mitochondria) DPTA diethylenetriaminepentacetic acid EGTA FCCP HEDTA Mes 4-morpholineethanesulphonic acid Mops 4-morpholinepropanesulphonic acid Tes 2-((2-hydroxy-1,1-bis(hydroxymethyl)ethyl)-amino)ethanesulphonic acid |
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