Effect of uncouplers on endogenous respiration and ferrous iron oxidation in a chemolithoautotrophic bacterium Acidithiobacillus (Thiobacillus) ferrooxidans.
Oxidation of ferrous iron (Fe2+) to ferric iron (Fe3+) with oxygen (O2) by Acidithiobacillus (Thiobacillus) ferrooxidans is considered to be inhibited by uncouplers. Oxidation of the endogenous substrates (presumably NADH) with O2 or Fe3+, on the other hand, was stimulated by uncouplers, 2,4-dinitrophenol (DNP) and carbonylcyanide-m-chlorophenyl-hydrazone (CCCP), as expected in respiratorily controlled mitochondria or heterotrophic bacteria. Amytal and rotenone were inhibitory. Fe3+ reduction by endogenous substrates was studied extensively and was found to be stimulated by a permeable anion, SCN- and weak acids, as well as the above uncouplers. Proton translocating properties of some of these stimulators were shown by following a pH change in the cell suspension. It was concluded that any compounds that destroy proton electrochemical gradient, Deltap, stimulated endogenous respiration. Stimulation of Fe2+ or ascorbate oxidation by lower concentrations of uncouplers was successfully demonstrated by shortening the reaction time, but only to a small extent. Uncouplers at concentrations stimulatory to endogenous respiration inhibited Fe2+ oxidation if present before Fe2+ addition. The inhibition by 10 microM CCCP was reversed by washing the cells in a buffer. Complex I inhibitors, atabrine, rotenone and amytal inhibited Fe2+ oxidation, more strongly in the presence of 0.1 mM DNP. It is proposed that Fe2+ oxidation required Deltap perhaps to climb an energetically uphill reaction or to reduce NAD+ to NADH by reversed electron flow for CO2 fixation. The latter interpretation implies some obligatory coupling between Fe2+ oxidation and NAD+ reduction.
Department of Microbiology, University of Manitoba, Winnipeg, MB, Canada R3T 2N2.
Yongqiang
Y
Chen
Isamu
I
Suzuki
D019297:2,4-Dinitrophenol / Q000494:pharmacology; D042763:Acidithiobacillus / Q000187:drug effects* / Q000378:metabolism*; D000143:Acids; D000654:Amobarbital / Q000494:pharmacology; D001205:Ascorbic Acid / Q000378:metabolism; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005290:Ferric Compounds / Q000378:metabolism; D005296:Ferrous Compounds / Q000378:metabolism*; D017879:Isothiocyanates; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D010085:Oxidative Phosphorylation / Q000187:drug effects; D010101:Oxygen Consumption / Q000187:drug effects*; D018892:Proton-Motive Force / Q000502:physiology; D011796:Quinacrine / Q000494:pharmacology; D012402:Rotenone / Q000494:pharmacology; D014475:Uncoupling Agents / Q000494:pharmacology*
D000143:Acids; D004791:Enzyme Inhibitors; D005290:Ferric Compounds; D005296:Ferrous Compounds; D017879:Isothiocyanates; D014475:Uncoupling Agents; D012402:Rotenone; D009243:NAD; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D000654:Amobarbital; D011796:Quinacrine; D001205:Ascorbic Acid; D019297:2,4-Dinitrophenol