Polyanion hydrophobicity and protein basicity affect protein stability in protein-polyanion complexes.

Stability of four dissimilar basic proteins (chymotrypsinogen A, ribonuclease A, cytochrome c, lysozyme) in the complex with four polyanions (heparin, poly(vinylsulfate), poly(4-styrene-sulfonate), Nafion) has been studied by differential scanning calorimetry. The polyanions were chosen because of their different charge density and hydrophobicity. Relative hydrophobicity of polyanions have been compared by three different parameters: (i) partition coefficient determined in octanol/water system, (ii) electrocapillary curves obtained by the method of controlled convection, and (iii) change in absorbance of small cationic amphiphilic molecule, aminoacridine, due to interaction with polyanion. Our results suggest that stability of proteins in the complex with polyanions negatively correlate with charge-related properties of the proteins such as isoelectric point and surface charge density and hydrophobicity of the polyanions.