Balanced biochemical reactions: a new approach to unify chemical and biochemical thermodynamics.

A novel procedure is presented which, by balancing elements and electric charge of biochemical reactions which occur at constant pH and pMg, allows assessing the thermodynamics properties of reaction Δ(r)G'⁰, Δ(r)H'⁰, Δ(r)S'⁰ and the change in binding of hydrogen and magnesium ions of these reactions. This procedure of general applicability avoids the complex calculations required by the use of the Legendre transformed thermodynamic properties of formation Δ(f)G'⁰, Δ(f)H'⁰ and Δ(f)S'⁰ hitherto considered an obligatory prerequisite to deal with the thermodynamics of biochemical reactions. As a consequence, the term "conditional" is proposed in substitution of "Legendre transformed" to indicate these thermodynamics properties. It is also shown that the thermodynamic potential G is fully adequate to give a criterion of spontaneous chemical change for all biochemical reactions and then that the use of the Legendre transformed G' is unnecessary. The procedure proposed can be applied to any biochemical reaction, making possible to re-unify the two worlds of chemical and biochemical thermodynamics, which so far have been treated separately.