Sulfide-dependent photosynthetic electron flow coupled to proton translocation in thylakoids of the cyanobacterium Oscillatoria limnetica

Yosepha Shahak, Boaz Arieli, Brian Binder, Etana Padan*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

Abstract

Light-induced proton translocation coupled to sulfide-dependent electron transport has been studied in isolated thylakoids of the cyanobacterium Oscillataria limnetica. The thylakoids are obtained by osmotic shock of washed spheroplasts, prepared with glycine-betaine as the osmotic stabilizer. 13C NMR studies suggests that betaine is the major osmoregulator in O. limnetica. Thylakoid preparations obtained from both sulfide-induced anoxygenic cells and noninduced oxygenic cells are capable of proton pumping coupled to phenazinemethosulfate-mediated cyclic electron flow. However, only in the induced thylakoids can sulfide-dependent proton gradient (ΔpH) formation be measured, using either NADP or methyl viologen as the terminal acceptor. Sulfide-dependent ΔpH formation correlates with a high-affinity electron donation site (apparent Km 44 μm at pH 7.9). This site is not lost upon washing of the thylakoids. In addition, both sulfide-dependent electron transport and ΔpH formation are sensitive to inhibitors of the cytochrome b6f complex such as 2-n-nonyl-4-hydroxyquinoline-N-oxide, 2,4-dinitrophenyl ether of 2-iodo-4-nitrothymol, or stigmatellin. Sulfide-dependent NADP photoreduction of low affinity (which does not saturate by as much as 7 mm sulfide) is detected in both induced and noninduced thylakoids, but this activity is insensitive to the inhibitors and is not coupled to proton transport. It is suggested that the adaptation of O. limnetica to anoxygenic photosynthesis involves the induction of a thylakoid factor(s) which creates a high-affinity site for sulfide, and the transfer of its electrons via the cytochrome b6f complex, coupled to proton translocation.

Original languageEnglish
Pages (from-to)605-615
Number of pages11
JournalArchives of Biochemistry and Biophysics
Volume259
Issue number2
DOIs
StatePublished - Dec 1987

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