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Biochemistry and Molecular Biology Education, Vol. 29 (3) (2001) pp. 101-103
© 2001 IUBMB. Published by Elsevier Science Ltd. All rights reserved.
PII: S1470-8175(01)00036-4

Article

The free energies of metabolic reactions (DeltaG) are not positive

Robert A. Edwards * redwards@ucalgary.ca

Division of Biochemistry, Faculty of Science, University of Calgary, Calgary, Alberta, Canada, T2N 1N4

Abstract

Biochemistry textbooks often erroneously state that some metabolic reactions have positive free energies (DeltaG), which suggests that they are spontaneous in the reverse direction. This incorrectly implies that reverse fluxes can occur through some steps in a metabolic pathway while the overall flux through the pathway is in the forward direction. In fact, at steady state all the reactions of a metabolic pathway proceed in the forward direction with the same flux. During periods of transition between steady states a positive free energy for any one reaction in a pathway means that the pathway is not actually proceeding from beginning to end.

Keywords: Free energy; Metabolic reactions; Metabolic flux; Thermodynamics

*Tel.: +1-403-220-5350

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