Abstract
A recent paper suggests that the water originating from the ATP production coupled to aerobic glucose oxidation causes more than a 6 fold increase in the production of metabolic water, compared with the standard textbook description of the oxidation process. However, the authors seem to have forgotten that the simultaneous processes of ATP utilization takes up the same amount of water, which was liberated during the ATP synthesis. Thus, at steady state, there is no net increase in the production of metabolic water.
In the paper by Dienel and Lauritzen [1], the sum-reaction of glucose oxidation in the cells of the brain is described as follows:
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1 |
However, the equation is incomplete. The process of ATP consumption is missing. The basic design of steady state aerobic energy metabolism in mammalian cells is to maintain matching rates of formation and utilization of ATP, and thereby maintaining a nearly constant ATP concentration. Thus, the extra 32 H2O in Eq. 1 is consumed by the simultaneously occurring hydrolysis of ATP in the same cell.
Therefore, if properly corrected, Eq. 1 translates into the standard textbook reaction [2] given below in Eq. 2, where the net water production is 6 H2O, but not 38 H2O.
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2 |
One interesting aspect, not touched upon, concerning metabolic water, is that the intracellular location of consumption and production of metabolic water might create a directional water flux in the cell. Albeit very small.
Author contributions
Bjørn Quistorff is the sole author.
Data availability
No datasets were generated or analysed during the current study.
Declarations
Competing interests
The authors declare no competing interests.
Footnotes
The online version of the original article can be found at 10.1186/s12987-025-00647-8.
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References
- 1.Dienel GA and Lauritzen M. A budget for brain metabolic water production by glucose catabolism during rest, rises in activity and sleep. In: Fluids and Barriers of the CNS; 2025, 22:44, 1–26. 10.1186/s12987-025-00647-8
- 2.Streyer L. Biochemistry, 2. edn.; 1981, Chap. 11, 235–54.
Associated Data
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Data Availability Statement
No datasets were generated or analysed during the current study.