Thermodynamics of Nath's 2-ion model for ATP synthesis

Abstract

A major finding of studies of organic acid ionization was that substituents on an aliphatic chain attached to a carboxyl group have large effects on the equilibrium constant but very little effect on Δ_ionizH which is in the range 0 ± 4 kJ/mol for all carboxylic acids of this type. According to Nath's 2-ion mechanism for ATP synthesis, succinic acid was selected by biological evolution because an acid that could be ionized with no energy input was required, i.e., with Δ_ionizH near zero. In support of this, ATP synthesis evolved in prokaryotes in a world without oxygen in the atmosphere and consequently catabolic reactions in prokaryotes that are coupled to ATP synthesis generally have small enthalpy changes. ATP synthesis in anaerobes is thus driven by the potential energy in concentration gradients. This potential energy is associated with a probability field quantified by the change in the number of microstates of particle distributions. ATP synthesis is thus powered by a probability field associated with a concentration gradient of ions consistent with Nath's 2-ion mechanism.

Keywords: Concentration gradients; Entropy of particle distribution; P/O ratios; Potential energy; Prokaryote bioenergetics.