Biochemical pH clamp: the forgotten resource in membrane bioenergetics

Area of Science:

• Plant Physiology
• Cellular Metabolism
• Bioenergetics

Background:

• Solute transport in plant cells relies on proton motive force (pmf), generated by a pH gradient and membrane potential.
• P-type H+ ATPases are traditionally considered the sole source of pmf, linking transport directly to ATP hydrolysis.
• Emerging evidence indicates that H+ pump activity alone may be insufficient to energize transport, particularly under stress.

Purpose of the Study:

• To investigate the role of metabolic buffering in maintaining the proton motive force (pmf) for plant cell solute transport.
• To explore the mechanisms of cytosolic H+ scavenging and apoplastic H+ generation.
• To discuss the thermodynamic implications of active buffering in plant bioenergetics.

Main Methods:

• Analysis of H+ transport mechanisms in plant cells.
• Investigation of metabolic pathways involved in H+ buffering (malic enzyme, GABA shunt, CO2 hydration).
• Thermodynamic modeling of active buffering processes.

Main Results:

• Metabolic processes, termed 'active buffering,' contribute significantly to stabilizing the pH gradient essential for pmf.
• Cytosolic H+ is scavenged via malate and glutamate decarboxylation.
• Apoplastic H+ is generated by CO2 conversion to bicarbonate during respiration.

Conclusions:

• Active metabolic buffering plays a critical role in energizing solute transport, complementing the function of H+ ATPases.
• Understanding these buffering mechanisms is vital for comprehending plant cell function, especially under environmental stress.
• The study highlights the complex interplay between metabolism, ion transport, and bioenergetics in plants.