Metabolic Processes Account for the Majority of Intracellular Water in Log-Phase Escherichia coli Cells as Revealed by Hydrogen Isotopes
It is generally believed that water transport across biological membranes is essentially a near-instantaneous process, with water molecules diffusing directly across the membrane as well as through pores such as aquaporins. As a result of these processes by which water can equilibrate across a membrane, a common assumption is that intracellular water is indistinguishable from extracellular water. To test this assumption directly, we measured the hydrogen isotope ratio of intracellular water in Escherichia coli cells. Our results demonstrate that over 50% of the intracellular water hydrogen atoms in log-phase E. coli cells are isotopically distinct from the growth medium water and that these isotopically distinct hydrogen atoms are derived from metabolic processes. As expected, the H/D isotope ratio of intracellular water from log-phase cells showed an appreciably larger contribution from metabolic water than did intracellular water from stationary-phase cells (53 ± 12% versus 23 ± 5%). The H/D isotope ratio of intracellular water was also monitored indirectly by measuring the isotope ratio of fatty acids, metabolites that are known to incorporate hydrogen atoms from water during biosynthesis. Significantly, the difference in the isotopic composition of intracellular water from log- to stationary-phase E. coli cells was reflected in the hydrogen isotope ratio of individual fatty acids harvested at the two different times, indicating that the isotope ratio of metabolites can be used as an indirect probe of metabolic activity. Together these results demonstrate that contrary to the common assumption that intracellular water is identical to extracellular water, these two pools of water can actually be quite distinct.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 944783
- Report Number(s):
- PNNL-SA-49820; TRN: US200902%%949
- Journal Information:
- Biochemistry, 45(45):13622-13630, Vol. 45, Issue 45
- Country of Publication:
- United States
- Language:
- English
Similar Records
/sup 35/Cl/sup -/ and /sup 2/H NMR measurement of intracellular water volume in renal proximal tubules
Detection of Metabolic Fluxes of O and H Atoms into Intracellular Water in Mammalian Cells