Abstract
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Neutron scattering, by using deuterium labelling, revealed how intracellular water dynamics,
measured in vivo in E. coli, human red blood cells and the extreme halophile, Haloarcula
marismortui, depends on the cell type and nature of the cytoplasm. The method uniquely
permits the determination of motions on the molecular length (Ba˚ ngstrøm) and time
(pico- to nanosecond) scales. In the bacterial and human cells, intracellular water beyond the
hydration shells of cytoplasmic macromolecules and membrane faces flows as freely as liquid
water. It is not ‘‘tamed’’ by confinement. In contrast, in the extreme halophile archaeon,
in addition to free and hydration water an intracellular water component was observed with
significantly slowed down translational diffusion. The results are discussed and compared to
observations in E. coli and Haloarcula marismortui by deuteron spin relaxation in NMR—a
method that is sensitive to water rotational dynamics on a wide range of time scales.