The Minimum Biological Energy Quantum

Volker Müller,Verena Hess

doi:10.3389/fmicb.2017.02019

Abstract

Some anaerobic archaea and bacteria live on substrates that do not allow the synthesis of one mol of ATP per mol of substrate via substrate level phosphorylation (SLP). Energy conservation in these cases is only possible by a chemiosmotic mechanism that involves the generation of an electrochemical ion gradient across the cytoplasmic membrane that then drives ATP synthesis via an ATP synthase. The minimal amount of energy required for ATP synthesis is thus dependent on the magnitude of the electrochemical ion gradient, the phosphorylation potential in the cell and the ion/ATP ratio of the ATP synthase. It was always thought that the minimum biological energy quantum is defined as the amount of energy required to translocate one ion across the cytoplasmic membrane. We will discuss the thermodynamics of the reactions involved in chemiosmosis and describe the limitations for ion transport and ATP synthesis that led to the proposal that at least −20 kJ/mol are required for ATP synthesis. We will challenge this hypothesis by arguing that the enzyme energizing the membrane may translocate net less than one ion: By using a primary pump connected to an antiporter module a stoichiometry below one can be obtained, implying that the minimum biological energy quantum that sustains life is even lower than assumed to date.

Highlights

The most important task of a cell is to divide and produce daughter cells
Most of the experiments at that time were done with cells that degraded an organic molecule such as, glucose via glycolysis and it turned out that some reactions of the glycolysis pathway are directly coupled to the synthesis of adenosine triphosphate (ATP) from ADP and inorganic phosphate (Pi) (Bücher and Pfleiderer, 1955)
It is clear that chemiosmosis provides about 89% of the ATP that is generated from the oxidation of one molecule glucose to CO2, it is the most important mechanism of ATP synthesis for a living cell

Summary

INTRODUCTION

The most important task of a cell is to divide and produce daughter cells. This requires the biosynthesis of macromolecules such as, lipids, proteins, and carbohydrates from smaller precursors. The ion/ATP stoichiometry is known (n = 3.3), we can calculate the μ Ion according to Equation (11) to −119 to −94 mV, the lowest value reported Substituting these values for μ Ion into Equation (10), we can calculate the actual amount of energy that is required to translocate one ion across the membrane: in this case, 11.5 to 9.1 kJ/mol are sufficient, due to the low μ Ion. IGP evolved very early in life history and enabled the first life forms to make a living from the oxidation of gaseous compounds such as, hydrogen, carbon monoxide, or formate, coupled to the reduction of, for example, CO2, Fe3+, or S0 (Martin et al, 2008; Lane and Martin, 2012). As discussed above, the value can be lower, and in situ analyses suggest that growth proceeds down to −10 kJ/mol (Hoehler et al, 2001)

G VALUE SUBSTRATES

Findings

CONCLUSION