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Functional Plant Biology Functional Plant Biology Society
Plant function and evolutionary biology
RESEARCH ARTICLE

Proton Translocation, Electron Transport and Phosphorylation in Isolated Chloroplasts

WS Chow and AB Hope

Australian Journal of Plant Physiology 4(4) 647 - 665
Published: 1977

Abstract

The steady-state rates of proton translocation (ΦH) associated with rates of light-induced electron transport (Φe) have been studied under a variety of conditions, with and without phosphorylation, in both spinach and pea chloroplasts, and using the absorbance changes of phenol red as a pH indicator. The method is discussed critically and compared with others. Using values of ΦH estimated from the initial efflux of H+ after continuous illumination for 17 s, it has been found that ΦHe increased to a maximum value of 2 under conditions which enhanced the permeability of membranes to H+ and a second ion. The maximum value of about 2 was observed over the whole pH range for which phenol red can be used as a pH indicator, namely pH 7.0 - 8.7. The stimulation of electron transport by phosphorylation was also studied with a view to enquiring into the ratio ΦHH/RATP, where ΦH is the proton flux via an ATPase giving rise to a phosphorylation rate RATP.

A scheme of the pathways of protons in the thylakoid membrane is proposed to account for the evariation of ΦHe under a large range of conditions. This scheme is in line with the 'bobbing up and down' hypothesis for the mechanism of active proton transport in energy-transducing membranes.

https://doi.org/10.1071/PP9770647

© CSIRO 1977

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