Partial purification and characterization of polyphenoloxidase from peppermint (Mentha piperita)

Polyphenoloxidase (PPO) of peppermint leaves (Mentha piperita) was isolated by (NH4)(2)SO4 precipitation and dialysis. Its pH and temperature optima w ere 7.0 and 30 degreesC, respectively. On heat-inactivation, half of the ac tivity was lost after 6.5 and 1.5 min of treatment at 70 and 80 degreesC, r espectively. Sucrose, (NH4)(2)SO4, NaCl and KCl appeared to be protective a gents of peppermint PPO against thermal denaturation. Km of this enzyme ran ged from 6.25 x 10(-3) M with catechol to 9.00 x 10(-3) M with L-dopa. The I-50 values of inhibitors studied on PPO were determined by means of activi ty percentage (I) diagrams. Values were 1.4 x 10(-4) M, 1.7 x 10(-4) M, 9.7 x 10(-5) M, 2.45 x 10(-4) M, 2.16 x 10(-1) M, 1.83 x 10(-5) M, 6.5 x 10(-5 ) M, 1.4x 10(-2) M, 7.5 x 10(-5) M, for potassium cyanide, glutathione, asc orbic acid, thiourea, sodium azide, sodium metabisulfite, dithioerythritol, beta -mercaptoethanol and sodium diethyl dithiocarbamate respectively, The refore, sodium metabisulfite was the most effective inhibitor. (C) 2001 Els evier Science Ltd. All rights reserved.