Electron transport pathways for the oxidation of endogenous substrate(s) in Acidithiobacillus ferrooxidans

Oxidation of endogenous substrate(s) of Acidithiobacillus ferrooxidans with O 2 or Fe 3+ as electron acceptor was studied in the presence of uncouplers and electron transport inhibitors. Endogenous substrate was oxidized with a respiratory quotient (CO 2 produced/O 2 consumed) of 1.0, indicating its carbohydrate nature. The oxidation was inhibited by complex I inhibitors (rotenone, amytal, and piericidin A) only partially, but piericidin A inhibited the oxidation with Fe 3+ nearly completely. The oxidation was stimulated by uncouplers, and the stimulated activity was more sensitive to inhibition by complex I inhibitors. HQNO (2-heptyl-4-hydroxyquinoline N-oxide) also stimulated the oxidation, and the stimulated respiration was more sensitive to KCN inhibition than uncoupler stimulated respiration. Fructose, among 20 sugars and sugar alcohols including glucose and mannose, was oxidized with a CO 2 /O 2 ratio of 1.0 by the organism. Iron chelators in general stimulated endogenous respiration, but some of them reduced Fe 3+ chemically, introducing complications. The results are discussed in view of a branched electron transport system of the organism and its possible control.Key words: Acidithiobacillus ferrooxidans, endogenous respiration, uncouplers, electron transport.