Protein and nucleic acid hydration and cosolvent interactions: establishment of reliable baseline values at high cosolvent concentrations.

Hydration and cosolvent interactions of biological macromolecules can be derived, subject to excluded volume corrections, from studies of density increments at constant chemical potentials of diffusible solutes through a semipermeable membrane. In addition to precision density determinations of solutions dialyzed to equilibrium, the analytical ultracentrifuge, static and dynamic light and small angle X-ray and neutron scattering, and combined pairwise use of, for instance, ultracentrifugation and neutron scattering, considerably strengthen the experimental analysis and its interpretation. We have examined hydration of bovine serum albumin (BSA) in the native and denatured states, and binding of the denaturant guanidinium chloride (GdmCl) to the latter form; hydration of DNA and interaction with NaCl and CsCl; revised values of the halophilic malate dehydrogenase (hMDH) tetramer hydration and 'binding' of salts; probing of nucleosome core particle hydration as distinct from and additionally to the evaluation of volume exclusion (holes), by use of variously sized sugar related probes. Conclusions presented are compared to results from precision calorimetry and from X-ray crystallography structures, whenever applicable, and comparisons made with alternative interpretations and experimental approaches.