Plastocyanin redox kinetics in spinach chloroplasts: evidence for disequilibrium in the high potential chain

• Published in: Biochimica et biophysica acta 2004-11, Vol.1659 (1), p.63-72
• Main Authors: Kirchhoff, Helmut, Schöttler, Mark Aurel, Maurer, Julia, Weis, Engelbert
• Format: Article
• Language: English
• Subjects: Chlorophyll - metabolism; Chloroplasts - physiology; Chloroplasts - radiation effects; Computer Simulation; Cytochromes f - metabolism; Diffusion; Homeostasis - physiology; Light; Models, Biological; Oxidation-Reduction; Photosystem I Protein Complex - metabolism; Photosystem I Protein Complex - radiation effects; Plant Leaves - physiology; Plant Leaves - radiation effects; Plastocyanin; Plastocyanin - metabolism; reaction kinetics; Redox equilibrium; redox reactions; Spinacia oleracea - metabolism; Spinacia oleracea - radiation effects; Thylakoids; Thylakoids - physiology; Thylakoids - radiation effects
• ISSN: 0005-2728; 0006-3002; 1879-2650
• DOI: 10.1016/j.bbabio.2004.08.004

Reduction kinetics of cytochrome f, plastocyanin (PC) and P 700 (‘high-potential chain’) in thylakoids from spinach were followed after pre-oxidation by a saturating light pulse. We describe a novel approach to follow PC redox kinetics from deconvolution of 810–860 nm absorption changes. The equilibration between the redox-components was analyzed by plotting the redox state of cytochrome f and PC against that of P 700. In thylakoids with (1) diminished electron transport rate (adjusted with a cytochrome bf inhibitor) or (2) de-stacked grana, cytochrome f and PC relaxed close to their thermodynamic equilibriums with P 700. In stacked thylakoids with non-inhibited electron transport, the equilibration plots were complex and non-hyperbolic, suggesting that during fast electron flux, the ‘high-potential chain’ does not homogeneously equilibrate throughout the membrane. Apparent equilibrium constants