Chemistry

   

Chemiosmosis and Microscopic Reversibility: Irreconcilable. Thermodynamic Limitations of Coupled Equilibria and the Role of Atp

Authors: Sosale Chandrasekhar

It is argued that the chemiosmotic theory, in positing the egress and ingress of protons across a membrane via different routes, violates the principle of microscopic reversibility (PMR). The theory was proposed as a mechanism for coupling the exergonic oxidation of NADH to the endergonic synthesis of ATP, believed to be a ready-to-use form of biochemical energy. The key proton-pump mechanism, however, should also operate in reverse by the PMR, hence is unlikely to be valid. Generally, the transfer of free energy via coupled equilibria is problematical, as neither of the coupled processes would go to completion. (However, it may be feasible in the case of entropy-driven reactions, as happens in the reactions of the Krebs cycle that lead to the formation of NADH.) Furthermore, reported thermodynamic data do not support the idea of ATP as a ‘high energy’ molecule, but rather indicate that ATP hydrolysis is driven by release of phosphate. In fact, many of the reactions believed to be thermodynamically driven by ATP hydrolysis are likely exergonic per se. ATP possibly provides part of the activation energy for the reaction in many cases. An alternative (non-equilibrium) mechanism for ATP synthesis is proposed based on the increase in pH that would accompany the oxidation of NADH. This would generate ADP3- and HPO42- which could form ATP4- in a thermodynamically favoured process within hydrophobic pockets.

Comments: 25 Pages.

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[v1] 2014-03-05 03:38:21

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