The absence of volume change in the gelation of hemoglobin-S

The volume change for the gelation of deoxygenated sickle cell hemoglobin has been measured by dilatometry at 22.0 degrees C and found to be zero. The precision of the result is 0 +/- 1.4 ml/mol of protein present in the sample. When the solubility of the protein is taken into account, the precision is 0 +/- 5.1 ml/mol of gelled hemoglobin. The participation of "hydrophobic interactions" in sickle cell hemoglobin gelation and model compound studies of the volume change associated with transferring hydrophobic solutes from an aqueous to a hydrophobic milieu, as well as the volume changes of other globular protein polymerizations, led us, initially, to expect a large positive delta V. The results are discussed in the context of concentration effects in sickle cell hemoglobin solutions and of recent work on the pressure-induced denaturation of globular proteins, which also gives smaller volume effects than had been anticipated.