Systems of biochemical reactions from the point of view of a semigrand partition function Original Research Article

Semigrand partition functions contain all the thermodynamic information on reaction systems. When they are written for systems at specified pH, they yield the transformed Gibbs energy G′ of the system and the thermodynamic properties that can be calculated from G′. When they are written for systems at specified pH and specified concentrations of coenzymes, they yield the further transformed Gibbs energy G″ and properties that can be calculated from G″. This is illustrated by considering: (1) a reactant that is a weak monoprotic acid at a specified pH; (2) a reaction between two pseudoisomer groups at a specified pH; and (3) the first five reactions of glycolysis. Equilibrium compositions in glycolysis are calculated at pH 7 and different steady-state concentrations of ATP and ADP.