Specific volume and compressibility of human serum albumin–polyanion complexes

The ultrasound velocimetry, densitometry, and differential scanning calorimetry have been used to study the formation of the complexes between human serum albumin (HSA) and polyanions heparin (HEP) and/or dextran sulfate (DS). The values of the ultrasound velocity and specific volume allowed us to determine the specific adiabatic compressibility, K/β0, which reflects the degree of volume compressibility of the complexes. We showed that in the presence of HEP and DS the adiabatic compressibility of HSA decreases with increasing concentration of polyanions. HEP more strongly interacts with HSA than DS. pH of electrolyte in the range 4.7–8.5 weakly affects the adiabatic compressibility. Changes of compressibility of HSA can be caused by increase of the hydration due to the formation of the HSA–polyanion complexes and due to partial unfolding of HSA. The HSA–polyanion interaction resulted in decrease of phase transition temperature of the protein. This evidences about protein destabilization in the presence of polyanions.