Energy coupling and thermokinetic balancing in enzyme kinetics. Microscopic reversibility and detailed balance revisited.

A survey of the development of the concepts of microscopic reversibility and detailed balancing is given. Considerable confusion surrounds these concepts. To obviate this, an unambiguous relation is presented that holds under all conditions and for which we propose the term "thermokinetic balancing." The utility of this relation, which in contrast to detailed balancing is independent of reactant and product concentrations, is demonstrated in a detailed discussion of the kinetics and thermodynamics of the calcium-transporting ATPase according to the principles worked out by Hill. This includes a critical analysis of the different concepts advocated by Jencks and Tanford. The advantage of thermokinetic balancing over detailed balancing is illustrated by examples, high-lighting the relationship of these procedures to standard free energies and basic free energies.