Determination of flux directions by thermodynamic network analysis: Computing informative metabolite pools

Network thermodynamics focuses on the energetic analysis of complex metabolic networks. The method connects free Gibbs energies, metabolite concentrations and flux directions by fundamental thermodynamic laws. Here, a new application of network thermodynamics is presented that identifies those metabolite pools that have to be measured in order to determine as many flux directions as possible. For a medium-scaled reaction network such informative metabolite pools are computed with an approach based on Monte Carlo sampling. It turns out that some reactions can be directed with only a few measurements whereas other reactions cannot be directed even with a complete data set. High connectivity in metabolic reaction networks in alliance with concentration ranges make it impossible to intuitively foresee such results. In particular, the impact of measurements of a special type of metabolites being involved in many reactions, so called energetic currency metabolites is investigated.