According to electrophoresis results, all the papain in the latex
was moved into PEG phase (Fig. 1), which represented ∼8%
of the total proteolytic activity in the papaya latex (Table 2).
All the PEG–(NH4)2SO4 systems except the system of 12%
PEG–9% (NH4)2SO4 provided pure papain in the top phase.
Interference with chymopapain was thus not noticed, as was the
case in PEG–phosphate system [19]. The remaining proteolytic
activity corresponding to chymopapain, glycyl endopeptidase
and caricain remained in the salt rich (bottom) phase (Fig. 1,
lane 5). The optimal conditions for extraction turned out to be
a two-phase system composed of 8% (w/w) PEG–15% (w/w)
(NH4)2SO4 and papaya latex containing 20–40 mg protein/ml
at pH 5 (Table 2). Furthermore, the pure papain was obtained in
a more concentrated form since the top phase volume was about
1/4th the volume of the whole system (top phase volume=6ml;
bottom phase volume = 25.5 ml).