Rate-limiting step in oxidation of physiological and artificial reductants by Azotobacter vinelandii membrane vesicles

Ronit Sagi-Eisenberg*, Menachem Gutman

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

The respiration of Azotobacter vinelandii membrane vesicles was investigated in order to determine the partial rates of electron fluxes at each segment of its branched respiratory chain. It is concluded that under physiological conditions only 20 to 30% of the total flux is carried through the c4, c5 → a1,o chain. Steady state analysis indicates that the limited capacity of the chain is due to the slow rate of oxidation of the cytochromes c by the a1,o oxidases. This rate-limiting step is bypassed by the artificial electron donors, ascorbate-2,6-dichlorophenol indophenol and ascorbate-N,N,N′,N′-tetramethyl-p-phenylenediamine, which directly reduce the highly active a1,o oxidases. During the oxidation of ascorbate-N,N,N′,N′-tetramethyl-p-phenylenediamine by the membrane vesicles, an accumulation of oxidized N,N,N′,N′-tetramethyl-p-phenylenediamine occurs. Such accumulation of positively charged molecules should lead to a generation of a membrane potential. This fact and previous data concerning coupling site III of A. vinelandii are discussed.

Original languageEnglish
Pages (from-to)470-476
Number of pages7
JournalArchives of Biochemistry and Biophysics
Volume197
Issue number2
DOIs
StatePublished - 15 Oct 1979

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