Purification and enzymatic characteristics of a novel polyphenol oxidase from lotus seed (Nelumbo nucifera Gaertn.)

A polyphenol oxidase (PPO) from lotus seed was purified by the procedures including ammonium sulphate precipitation and affinity chromatography. The apparent molecular mass was 38.6 kDa by SDS-PAGE. Kinetic studies showed that the K-m and V-max values for catechol were 6.04mm and 416.67U, respectively. The PPO performed optimal activity in 20 degrees C and pH 7.0. The enzymatic activity could be mainly maintained up to 50 degrees C and pH 4.0-7.0. The activity could be inhibited by various inhibitors including thiourea, urea, sodium hydrogen sulphite, EDTA2Na, SDS, citric acid, guanidine hydrochloride, ascorbic acid, sodium sulphite and sodium thiosulphate. The metal ions Ba2+, Mg2+, Ca2+, Mn2+, Co2+ and Zn2+ could inhibit the activity of PPO, while Cu2+ performed obvious enhancement. The enzymatic properties of PPO could probably provide practical application in inhibiting the PPO activity and preventing enzymatic browning in the process of picking, transportation, processing and storage of fresh lotus seeds.