Cathodic polyacrylamide gel electrophoresis of papain during purification by two-step salt precipitation and extraction in aqueous two-phase system consisting of 8% PEG–15% (NH4)2SO4. The samples in the different lanes represent: standard papain (lane 1, 6 _g), crude latex extract (lane 2), purified papain from a two-step salt precipitation (lane 3), and from top phase of the system consisting of 8% (w/w) PEG–15% (w/w) (NH4)2SO4 (lane 4), and bottom phase of the same two-phase system (lane 5) after partitioning of latex.