Plackett-Burman design matrix with papain purity and activity recovery.

A: initial protein concentration at a low level (−1) of 10 mg/ml and a high level (+1) of 15 mg/ml; B: PEG molecular weight at a low level (−1) of 4000 Da and a high level (+1) of 6000 Da; C: PEG concentration at a low level (−1) of 10% (w/w) and a high level (+1) of 16% (w/w); D: phase forming salt at a low level (−1) of (NH4)2SO4 and a high level (+1) of NaH2PO4/K2HPO4; E: salt concentration at a low level (−1) of 10% (w/w) and a high level (+1) of 14% (w/w); F: temperature at a low level (−1) of 4°C and a high level (+1) of 20°C; G: pH at a low level (−1) of 6 and a high level (+1) of 8; H and I represent dummy variables.
*Determined by FPLC.
**Calculated by total activity of PEG phase/total activity of enzyme solution.