Specific cellular water dynamics observed in vivo by neutron scattering and NMR.

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.