Half a Century of Pursuing the Pervasive Proton

Abstract

Acid–base regulation is probably a universal attribute of life, and energy coupling via transmembrane H+ gradients is very widespread. Much of my academic career has been related to these two processes and to their interactions. Highlights from my studies of acid–base regulation are the quantitative resolution of the challenges for acid–base regulation in land plant shoots when metabolism involving net H+ production (e.g. primary assimilation of NH 4 + , NH3 or N2) occurs there, quantitation of the energy costs of acid–base regulation for different locations and mechanisms of acid–base regulation for the assimilation of a range on N sources and the interaction of CO2 concentrating mechanisms in aquatic photosynthetic organisms with acid–base regulation. Research on the significance of transmembrane H+ gradients has included a significant contribution to the early development of chemiosmotic hypothesis of polar transport of indoleacetic acid, the evolutionary significance of chemiosmotic coupling and the role of H+ leakage relative to other processes which consumed energy at an essentially constant rate regardless of the rate of light energy supply in determining the minimum photon flux density at which photolithotrophic growth can occur. On a global scale, work on the effects of anthropogenic CO2 production on ocean acid–base balance has helped to set limits on the significance of this ‘ocean acidification’ for marine algae. A final point covered in the chapter is an analysis of the continuing attempts to determine precisely what is being regulated, e.g. the pH of the intracellular compartment or the ionisation state of one or more of weak electrolytes in the compartment.