Salting-out behaviour of the domains of ovomucoid.

The solubility of ovomucoid and of four fragments comprising domain I, I+II, and III of the protein in concentrated ammonium sulphate solution were studied at different pHs (25 degrees C) and at various temperatures (pH 7.0), and the salting-out parameters Ks and beta were determined for the five proteins. The aqueous solubilities of ovomucoid and the four fragments were highly dependent on temperature which causes structural alteration due to thermal unfolding of the proteins. The values of KS and beta for domain III and domain II+III at different pHs were similar to those of other globular proteins whereas those of ovomucoid and domain I and domain I+II were atypical. They were explained in terms of the lack of structural stability and the presence of carbohydrate moieties in domains I and II.