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Journal article

Reversible redox energy coupling in electron transfer chains

Schagger H, Cramer W, Vonjagow G ...see all

Analytical Biochemistry, vol. 217, issue 2 (1994) pp. 220-230

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Abstract

Reversibility is a common theme in respiratory and photosynthetic systems that couple electron transfer with a transmembrane proton gradient driving ATP production. This includes the intensely studied cytochrome bc1, which catalyses electron transfer between quinone and cytochrome c. To understand how efficient reversible energy coupling works, here we have progressively inactivated individual cofactors comprising cytochrome bc1. We have resolved millisecond reversibility in all electron-tunnelling steps and coupled proton exchanges, including charge-separating hydroquinone-quinone catalysis at the Q(o) site, which shows that redox equilibria are relevant on a catalytic timescale. Such rapid reversibility renders popular models based on a semiquinone in Q(o) site catalysis prone to short-circuit failure. Two mechanisms allow reversible function and safely relegate short-circuits to long-distance electron tunnelling on a timescale of seconds: conformational gating of semiquinone for both forward and reverse electron transfer, or concerted two-electron quinone redox chemistry that avoids the semiquinone intermediate altogether.

Author-supplied keywords

  • adenosine triphosphate
  • adenosine triphosphate metabolism
  • catalysis
  • coenzymes
  • coenzymes metabolism
  • cytochrome b group
  • cytochrome b group genetics
  • cytochrome b group metabolism
  • cytochromes c
  • cytochromes c metabolism
  • electron transport
  • electron transport complex iii
  • electron transport complex iii genetics
  • electron transport complex iii metabolism
  • heme
  • heme analogs & derivatives
  • heme genetics
  • heme metabolism
  • hydrogen ion concentration
  • hydroquinones
  • hydroquinones metabolism
  • kinetics
  • photosynthesis
  • protons
  • rhodobacter capsulatus
  • rhodobacter capsulatus genetics
  • rhodobacter capsulatus metabolism
  • thermodynamics

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Authors

  • H. Schagger

  • W.A. Cramer

  • G. Vonjagow

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