Entropy Production and Its Application to the Coupled Nonequilibrium Processes of ATP Synthesis

Starting from the universal concept of entropy production, a large number of new results are obtained and a wealth of novel thermodynamic, kinetic, and molecular mechanistic insights are provided into the coupling of oxidation and ATP synthesis in the vital process of oxidative phosphorylation (OX PHOS). The total dissipation, Φ , in OX PHOS with succinate as respiratory substrate is quantified from measurements, and the partitioning of Φ into the elementary components of ATP synthesis, leak, slip, and other losses is evaluated for the first time. The thermodynamic efficiency, η , of the coupled process is calculated from the data on Φ and shown to agree well with linear nonequilibrium thermodynamic calculations. Equations for the P/O ratio based on total oxygen consumed and extra oxygen consumed are derived from first principles and the source of basal (state 4) mitochondrial respiration is postulated from molecular mechanistic considerations based on Nath’s two-ion theory of energy coupling within the torsional mechanism of energy transduction and ATP synthesis. The degree of coupling, q , between oxidation and ATP synthesis is determined from the experimental data and the irreversible thermodynamics analysis. The optimality of biological free energy converters is explored in considerable detail based on (i) the standard biothermodynamic approach, and (ii) a new biothermokinetic approach developed in this work, and an effective solution that is shown to arise from consideration of the molecular aspects in Nath’s theory is formulated. New experimental data in state 4 with uncouplers and redox inhibitors of OX PHOS and on respiratory control in the physiological state 3 with ADP and uncouplers are presented. These experimental observations are shown to be incompatible with Mitchell’s chemiosmotic theory. A novel scheme of coupling based on Nath’s two-ion theory of energy coupling within the torsional mechanism is proposed and shown to explain the data and also pass the test of consistency with the thermodynamics, taking us beyond the chemiosmotic theory. It is concluded that, twenty years since its first proposal, Nath’s torsional mechanism of energy transduction and ATP synthesis is now well poised to catalyze the progress of experimental and theoretical research in this interdisciplinary field.

Revisiting Mitchell’s chemiosmotic theory in light of new stoichiometric reaction equations of ATPase II

Chemiosmotic theory has been reining the field of bioenergetics since its inception. As stoichiometric mechanisms of the underlying chemical reactions have now been elucidated, it calls for a revision in the relationships derived by Mitchell in his seminal review paper. Here in this work, new formulation of the relationship between the pH difference and transmembrane potential, as derived in light of modified ATPase II reaction stoichiometry, has been proposed for the first time. This formulation results in accurate estimation of dependence of transmembrane potential on the pH difference across the two sides of the mitochondrial membrane. Thus, this work is of potential interest and will enable researchers working in the field of bioenergetics involving chemiosmotic theory to come-up with more exact mechanistic explanations.

An update of the chemiosmotic theory as suggested by possible proton currents inside the coupling membrane

Understanding how biological systems convert and store energy is a primary purpose of basic research. However, despite Mitchell's chemiosmotic theory, we are far from the complete description of basic processes such as oxidative phosphorylation (OXPHOS) and photosynthesis. After more than half a century, the chemiosmotic theory may need updating, thanks to the latest structural data on respiratory chain complexes. In particular, up-to date technologies, such as those using fluorescence indicators following proton displacements, have shown that proton translocation is lateral rather than transversal with respect to the coupling membrane. Furthermore, the definition of the physical species involved in the transfer (proton, hydroxonium ion or proton currents) is still an unresolved issue, even though the latest acquisitions support the idea that protonic currents, difficult to measure, are involved. Moreover, F o F 1 -ATP synthase ubiquitous motor enzyme has the peculiarity (unlike most enzymes) of affecting the thermodynamic equilibrium of ATP synthesis. It seems that the concept of diffusion of the proton charge expressed more than two centuries ago by Theodor von Grotthuss is to be taken into consideration to resolve these issues. All these uncertainties remind us that also in biology it is necessary to consider the Heisenberg indeterminacy principle, which sets limits to analytical questions.

Chemiosmotic coupling in oxidative phosphorylation: The history of a hard experimental effort hampered by the Heisenberg indeterminacy principle

Understanding how biological systems convert and store energy is a primary goal of biological research. However, despite the formulation of Mitchell’s chemiosmotic theory, which allowed taking fundamental steps forward, we are still far from the complete decryption of basic processes as oxidative phosphorylation (OXPHOS) and photosynthesis. After more than half a century, the chemiosmotic theory appears to need updating, as some of its assumptions have proven incorrect in the light of the latest structural data on respiratory chain complexes, bacteriorhodopsin and proton pumps. Moreover, the existence of an OXPHOS on the plasma membrane of cells casts doubt on the possibility to build up a transversal proton gradient across it, while paving the way for important applications in the field of neurochemistry and oncology. Up-to date biotechnologies, such as fluorescence indicators can follow proton displacement and sinks, and a number of reports have elegantly demonstrated that proton translocation is lateral rather than transversal with respect to the coupling membrane. Furthermore, the definition of the physical species involved in the transfer (proton, hydroxonium ion or proton currents) is still unresolved even though the latest acquisitions support the idea that protonic currents, difficult to measure, are involved. It seems that the concept of diffusion of the proton expressed more than two centuries ago by Theodor von Grotthuss, is decisive for overcoming these issues. All these uncertainties remember us that also in biology it is necessary to take into account the Heisenberg indeterminacy principle, that sets limits to analytical questions.

Chemiosmotic coupling in oxidative phosphorylation: The history of a hard experimental effort hampered by the Heisenberg indeterminacy principle

Understanding how biological systems convert and store energy is a primary goal of biological research. However, despite the formulation of Mitchell’s chemiosmotic theory, which allowed taking fundamental steps forward, we are still far from the complete decryption of basic processes as oxidative phosphorylation (OXPHOS) and photosynthesis. After more than half a century, the chemiosmotic theory appears to need updating, as some of its assumptions have proven incorrect in the light of the latest structural data on respiratory chain complexes, bacteriorhodopsin and proton pumps. Moreover, the existence of an OXPHOS on the plasma membrane of cells casts doubt on the possibility to build up a transversal proton gradient across it, while paving the way for important applications in the field of neurochemistry and oncology. Up-to date biotechnologies, such as fluorescence indicators can follow proton displacement and sinks, and a number of reports have elegantly demonstrated that proton translocation is lateral rather than transversal with respect to the coupling membrane. Furthermore, the definition of the physical species involved in the transfer (proton, hydroxonium ion or proton currents) is still unresolved even though the latest acquisitions support the idea that protonic currents, difficult to measure, are involved. It seems that the concept of diffusion of the proton expressed more than two centuries ago by Theodor von Grotthuss, is decisive for overcoming these issues. All these uncertainties remember us that also in biology it is necessary to take into account the Heisenberg indeterminacy principle, that sets limits to analytical questions.