Excluded volume effects on the partition of macromolecules between two liquid phases

Partition parameters of several proteins and other macromolecules are measured in an aqueous two-phase liquid system containing polyethylene glycol and phosphate buffer. Distribution of macromolecules is a function of the relative volume excluded to the macromolecules in the two phases. A simple model with no adjustable parameters yields covolumes of the macromolecules with the polyethylene glycol. Covolumes are used to estimate effective molecular volumes and the magnitudes of excluded volume effects. The same approach is applied to mixtures of macromolecules.