The Effect of Oxygen on Tetrathionate Reductase Activity and Biosynthesis

Abstract

S U M M A R YCyanide (I mM) strongly inhibited aerobic respiration, and 2,4 dinitrophenol (0.2 mM) apparently uncoupled oxidative phosphorylation, in nongrowing Citrobacter. At these inhibitor concentrations, anaerobic tetrathionate reductase activity was not much affected. Aeration inhibited tetrathionate reductase activity; 0.2 m~-2 , 4 DNP did not influence oxygen inhibition, but I mM-KCN restored the reductase activity quantitatively. The process of aerobic respiration rather than the oxygen molecule itself therefore inhibits tetrathionate reductase activity. Induced synthesis of reductase required anaerobic conditions. Cyanide and 2,4 DNP allowed anaerobic synthesis of reductase; aeration prevented it. This effect of oxygen was abolished neither by KCN nor by 2,4 DNP. Oxygen therefore represses the synthesis of tetrathionate reductase directly.

Tetrathionate reduction and production of hydrogen sulfide from thiosulfate.

“…Several aspects of the regulation of tetrathionate reduction are consistent with an overall picture of respiratory control in which there is a hierarchy of electron transport pathways, each of which represses all systems with lower energy potential and is, similarly, repressed during operation of the higher-energy-potential systems. In accordance with this picture, neither tetrathionate nor thiosulfate reduction occurs in the presence of oxygen (33,65,112,123,145) or nitrate (2,34). Oxygen has also been shown to prevent expression of P-galactosidase activity in Mu dl(lac) insertion mutants affected in the production of H2S from thiosulfate (3; Clark and Barrett, submitted).…”

“…Oxygen was shown to interfere with tetrathionate reduction by extracts of C. freundii (65,121). Kapralek and Pichinoty (65) attributed the effect to the preferential transfer of electrons to oxygen rather than to a direct effect of oxygen on the enzyme because cyanide prevented the inhibition, and the inhibition was reversible.…”

“…Furthermore, tetrathionate reduction prevents hydrogen evolution via the formate hydrogenlyase system (33,34,71,122), while thiosulfate reduction, a reaction of very low redox potential, can occur simultaneously with hydrogen evolution (34,71). Oxygen per se is reported to repress the synthesis of tetrathionate reductase (33, 34, 65), but it does not inhibit enzyme activity; however, electron transport to oxygen reversibly inhibits the activity in vitro (65,121). On the other hand, both inhibition and repression by nitrate occur only when nitrate respiration is possible (2,34,145).…”

Separation and distribution of thiosulfate-oxidizing enzyme, tetrathionate reductase, and thiosulfate reductase in extracts of marine heterotroph strain 16B

“…This indicates repression of the 16B enzymes by oxygen and is consistent with oxygen repression of inducible TTRs from Salmonella sp. (19) and C. freundii (7) as well as TTR and TSR from P. mirabilis (5). Both TTR and TSR in 16B are involved in anaerobic respiration (34).…”

Two sites of oxygen control in induced synthesis of respiratory nitrate reductase in Escherichia coli

“…The opinions reported thus far are contradictory and may be summarized as follows. (i) Oxygen itself is the corepressor (8,16). (ii) Electron transport to oxygen rather than oxygen itself regulates enzyme formation by blocking its assembly into the membrane-bound active form (1-3, 5, 20).…”