Abstract
The eQuilibrator component contribution method allows calculation of the overall Gibbs energy changes for conversion of glucose to a wide range of final products in the absence of other oxidants. Values are presented for all possible combinations of products with up to three carbons and selected others. The most negative Gibbs energy change is for the formation of graphite and water (−499 kJ mol–1) followed by CH4 and CO2 (−430 kJ mol–1), the observed final products of anaerobic digestion. Other favored products (with various combinations having Gibbs energy changes between −300 and −367 kJ mol–1) are short-chain alkanes, fatty acids, dicarboxylic acids, and even hexane and benzene. The most familiar products, lactate and ethanol + CO2, are less favored (Gibbs energy changes of −206 and −265 kJ mol–1 respectively). The values presented offer an interesting perspective on observed metabolism and its evolutionary origins as well as on cells engineered for biotechnological purposes.
Highlights
There is a long history of using thermodynamic analysis to aid our understanding of metabolism
Methods have been developed to give fairly accurate predictions of Gibbs energies of formation of a wide range of compounds of biochemical relevance with their chemical structure as the only input required.[3−9] These methods have been exploited for thermodynamic analysis of a variety of actual and hypothetical metabolic pathways and networks.[10−15] For example, it can be shown that the classic EMP glycolysis pathway is optimal for the conversion of glucose to lactate.[16]
This paper presents the overall Gibbs energy changes for conversion of glucose into all possible combinations of compounds having up to three carbon atoms and some selected larger molecules
Summary
There is a long history of using thermodynamic analysis to aid our understanding of metabolism. The overall Gibbs energy change for this process can be calculated, independent of whatever might be the exact metabolic pathway involved This approach has been used to assess the feasibility of formation of various end products by rumen microbes.[17] It has been applied to the possible formation of various industrial chemicals by engineered organisms.[18] It is interesting to use these prediction methods to consider the choice of overall end products of sugar fermentation under anaerobic conditions (and in the absence of other oxidizing species such as nitrate or sulfate). This paper presents the overall Gibbs energy changes for conversion of glucose into all possible combinations of compounds having up to three carbon atoms and some selected larger molecules These values have been calculated because they should be useful in analyzing the extent to which the overall Gibbs energy change has been a driver in the evolution of anaerobic metabolism. The values highlight some options for metabolic engineering and synthetic biology, showing that some practically interesting end products are thermodynamically favored
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