Photophosphorylation associated with synchronous turnovers of the electron-transport carriers in chloroplasts

Thomas Graan, Donald Richard Ort

Research output: Contribution to journalArticlepeer-review

Abstract

Two saturating single-turnover flashes spaced 100 ms apart are sufficient to achieve ATP formation in isolated chloroplast thylakoids. Two turnovers of the electron carriers result in the accumulation of about 7 nmol H+ / mg chlorophyll. Under the same conditions (i.e., ΔGATP = 38 kJ/mol) a solitary flash is inadequate to produce ATP. The electron flux from the third or any subsequent flash is coupled to ATP formation as efficiently as is observed in continuous light (i.e., ATP 2e > 1.0) and produces 0.8 molecules of ATP per coupling factor on each turnover. The yield of ATP per flash increases with declining temperature being largest near 4°C, the lowest value tested. The number of H+ accumulated per flash is independent of temperature so the greater yields of ATP near 4°C indicate that fewer H+ are existing the membrane via nonproductive pathways. The yield of ATP per flash near 4°C is largely independent of flash frequency between 1 and 30 Hz. When the formation of an electrical potential difference is prevented by adequate amounts of valinomycin and potassium the accumulated effects of about eight flashes are required before ATP formation is achieved (i.e., about 26 nmol H+/mg chlorophyll), indicating an average ΔpH/flash in excess of 0.3 units. In the presence of the exchange carrier nigericin, the electrical component of the driving force for ATP formation is enhanced at the expense of the ΔpH. In this case, ATP formation is efficiently coupled to electron flux only at flash frequencies rapid enough to allow a summation of the electrical field. These results clearly demonstrate that any processes which are prerequisites for ATP synthesis (i.e., activation of coupling factor or generation of Δp) are fulfilled by a remarkably small number of charge separations.

Original languageEnglish (US)
Pages (from-to)395-403
Number of pages9
JournalBBA - Bioenergetics
Volume682
Issue number3
DOIs
StatePublished - Dec 15 1982
Externally publishedYes

Keywords

  • (Spinach chloroplast)
  • Coupling factor
  • Membrane potential
  • Photophosphorylation
  • Photosynthesis
  • pH gradient

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

Fingerprint Dive into the research topics of 'Photophosphorylation associated with synchronous turnovers of the electron-transport carriers in chloroplasts'. Together they form a unique fingerprint.

Cite this