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Consistent Estimation of Gibbs Energy Using Component Contributions

Figure 2

An example of a futile cycle where Gibbs energies are derived using RC and GC.

The combined stoichiometry of (1) threonine aldolase, (2) acetaldehyde dehydrogenase (acetylating), (3) glycine C-acetyltransferase, and (4) threonine:NAD oxidoreductase creates a futile cycle where all the inputs and outputs are balanced. Using RC we are able to derive the of reactions 1 and 2 (green), but since 2-amino-3-oxobutanoate does not appear in formation energy tables – we must use GC for reactions 3 and 4 (magenta). The sum of all in this case is −6.0 kJ/mol which is a violation of the first law of thermodynamics.

Figure 2

doi: https://doi.org/10.1371/journal.pcbi.1003098.g002