Thermodynamics of monoclonal and mixed cryoimmunoglobin solubilization

The direct calorimetric determination of heats of solution for four monoclonal and three mixed (IgM/IgG) cryoglobulins is described. Values obtained by differential scanning calorimetry (DSC) are compared to values of the apparent delta Hsol obtained by a polyethylene glycol (PEG) precipitation method. The four monoclonal cryoglobulins manifest heats of solution determined by DSC to be of the same order of magnitude as heats obtained by PEG precipitation, although DSC values were 25 to 125% lower than the corresponding van't Hoff enthalpies. Values of delta Hsol for mixed cryoglobulins were significantly greater than monoclonal cryoglobulins on a molar basis. These higher values are primarily attributed to the greater surface area of these complexes which results in more extensive contact between molecules in the solid phase. No evidence was found that conformational changes contributed to the calorimetric delta Hsol values employing a variety of spectroscopic methods.