Reduction of protein volume and compressibility by macromolecular cosolvents: dependence on the cosolvent molecular weight.

The partial specific volume (V) and adiabatic compressibility (beta) of myoglobin have been shown to be reduced by small cosolvents such as glycerol (A. Priev, A. Almagor, S. Yedgar, B. Gavish, Biochemistry 35 (1996) 2061-2066). To elucidate the effect of the cosolvent size on these protein properties, in the present study we determined V and beta of myoglobin in solutions containing a homologous cosolvent series from sucrose to dextran--500 (M.W. 500,000). It was found that in addition to the expected effect of the cosolvent concentration, V and beta decrease with increasing cosolvent M.W. This suggests that structural properties of the cosolvent contribute to its effect on the protein interior.