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Research Paper |
Department of Biology, University of Bologna, 42 Irnerio, 40126 Bologna I, Italy1
Author for correspondence: Davide Zannoni. Tel: +39 051 209 1285/86. Fax+39 051 24 25 76. e-mail: zannoni{at}alma.unibo.it
The respiratory chain of Pseudomonas pseudoalcaligenes KF707 in membranes isolated from cells grown in the presence or absence of the toxic oxyanion tellurite (
) was examined. Aerobic growth in the absence of tellurite shows an NADH-dependent respiration which is 80% catalysed by the cytochrome (cyt) bc1-containing pathway leading to two terminal membrane-bound cyt c oxidases inhibited by different concentrations of KCN (IC50 0·2 and 1 µM). A third oxidase, catalysing the remaining 20% of the cyanide-resistant respiration and fully inhibited by 2–3 mM KCN, is also present; this latter pathway accounts for 60–70% of the total NADH-dependent respiration in membranes from cells grown in LB medium supplemented with potassium tellurite (35 µg ml-1). Two high-potential b-type haems (Em,7 +395 and 318 mV) are redox centres of a membrane-bound cyt c oxidase (possibly of the cbb3 type) which shows a 50% decrease of its activity in parallel with a similar decrease of the c-type haem content (mostly soluble cyt c) in membranes from tellurite-grown cells; the latter type of cells specifically contain a cyt b type at +203 mV (pH 9·0) which is likely to be involved in cyanide-resistant respiration. Comparison of the growth curve of KF707 cells in parallel with tellurite uptake showed that intracellular accumulation of tellurium (Te0) crystallites starts from the mid-exponential growth phase, whereas tellurite-induced changes of the respiratory chain are already evident during the early stages of growth. These data were interpreted as showing that reduction of tellurite to tellurium and tellurite-dependent modifications of the respiratory chain are unrelated processes in P. pseudoalcaligenes KF707.
Keywords: cytochromes, tellurite uptake, tellurium crystallites
Abbreviations: cyt, cytochrome; TMBZ, 3,3',5,5'-tetramethylbenzidine
This work is dedicated to my friend and colleague Franco Tatò, prematurely deceased on 7 July 2001.
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