One-step purification and freeze stability of papain at acidic pH values

Papain is a proteolytic enzyme of great commercial value. It is a cysteine protease highly expressed in Carica papaya fruit latex, but also present in papaya leaves. Purification procedures mostly deal with the latex and include a combination of precipitation and/or chromatographic techniques. Due to its solubility, structure and activity characteristics, the pH and salt content play significant roles in handling papain extracts. Here we report a simple, rapid and easily scalable procedure for papain purification from papaya leaves, which contain different contaminants as compared to papaya latex. Sodium chloride precipitation of contaminants at pH 5 followed by ammonium sulphate precipitation resulted in the removal of other leaf proteins and protein fragments from papain solution and about a 3-fold purification. The procedure also benefits from the suppression of autoproteolysis and preservation of the native structure, as confirmed by FTIR analysis, and the high recovery of activity of over 80%.