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. 1983 Oct;80(20):6249–6253. doi: 10.1073/pnas.80.20.6249

Spectrally distinct cytochrome b-563 components in a chloroplast cytochrome b—f complex: Interaction with a hydroxyquinoline N-oxide

Robert D Clark 1, Geoffrey Hind 1,*
PMCID: PMC394273  PMID: 16593381

Abstract

The two heme equivalents of cytochrome b-563 in the photosynthetic cytochrome b—f complex can be distinguished by their rate of reduction with dithionite at 25°C and by their optical absorption spectra at 77 K. The cytochrome b component that is rapidly reduced after addition of dithionite or reduced ferredoxin possesses an α band that splits at 77 K into two peaks, at 557 and 561 nm. Prolonged incubation with reductant reveals a second, approximately equimolar cytochrome b component that has at 77 K an unsplit α-band maximum at 561 nm. The designations cytochrome b-563H and cytochrome b-563L, respectively, are proposed for the rapidly and more slowly reduced cytochrome b-563 components. Potentiometric titration establishes a midpoint potential, Em, of -30 mV (electron change n ≈ 2) for cytochrome b-563H and -150 mV (n = 1) for cytochrome b-563L at pH 7.5. The reduction potential of these components is raised by 2-heptyl-4-hydroxyquinoline N-oxide, giving Em values of +57 and -34 mV, respectively, with each titration slope approximating n = 2.

Keywords: photosynthetic electron transport, plastoquinol:plastocyanin oxidoreductase, 2-heptyl-4-hydroxyquinoline N-oxide

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Selected References

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