Light and heavy water are often used interchangeably in
spectroscopic experiments with the tacit assumption that the structure of the
investigated biomolecule does not depend too much on employing one or the
other solvent. While this may often be a good approximation, we demonstrate
here using molecular dynamics simulations incorporating nuclear quantum
effects via modification of the interaction potential that there are small but
significant differences. Namely, as quantified and discussed in the present study,
both proteins and biomembranes tend to be slightly more compact and rigid in
D2O than in H2O, which reflects the stronger hydrogen bonding in the former
solvent.