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Biochemical pH clamp: the forgotten resource in membrane bioenergetics
Author(s) -
Wegner Lars H.,
Shabala Sergey
Publication year - 2020
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.16094
Subject(s) - apoplast , cytosol , biophysics , decarboxylation , chemistry , biochemistry , membrane potential , tricarboxylic acid , bicarbonate , atpase , citric acid cycle , membrane , metabolism , biology , enzyme , cell wall , organic chemistry , catalysis
Summary Solute uptake and release by plant cells are frequently energized by coupling to H + influx supported by the proton motive force (pmf). The pmf results from a stable pH difference between the apoplast and the cytosol, with bulk values ranging from 4.9 to 5.8 and from 7.1 to 7.5, respectively, in combination with a negative electrical membrane potential. The P‐type H + ATPases pumping H + from the cytosol into the apoplast at the expense of ATP hydrolysis are generally viewed as the only pmf source, exclusively linking membrane transport to energy metabolism. However, recent evidence suggests that pump activity may be insufficient to energize transport, particularly under stress conditions. Indeed, cytosolic H + scavenging and apoplastic H + generation by metabolism (denoted as ‘active’ buffering in contrast to the readily exhausted ‘passive’ matrix buffering) also stabilize the pH gradient. In the cytosol, H + scavenging is mainly associated with malate decarboxylation catalyzed by malic enzyme, and via the GABA shunt of the tricarboxylic acid (TCA) cycle involving glutamate decarboxylation. In the apoplast, formation of bicarbonate from CO 2 , the end‐product of respiration, generates H + at pH ≥ 6. Membrane potential is stabilized by K + release and/or by anion uptake via ion channels. Finally, thermodynamic aspects of active buffering are discussed.