Differential in vitro inhibition of polyphenoloxidase from a wild edible mushroom Lactarius salmonicolor

The polyphenol oxidase (LsPPO) from a wild edible mushroom Lactarius salmonicolor was purified using a Sepharose 4B-L-tyrosine-p-amino benzoic acid affinity column. At the optimum pH and temperature, the KM and VMax values of LsPPO towards catechol, 4-methylcatechol and pyrogallol were determined as 0.025M 0.748EU/mL, 1.80910-3 M 0.723EU/mL and 9.46510-3 M 0.722EU/mL, respectively. Optimum pH and temperature values of LsPPO for the three substrates above ranged between the pH 4.5-11.0 and 5-50C. Enzyme activity decreased due to heat denaturation with increasing temperature. Effects of a variety of classical PPO inhibitors were investigated opon the activity of LsPPO using catechol as the substrate. IC50 values for glutathione, p-aminobenzenesulfonamide, L-cysteine, L-tyrosine, oxalic acid, -mercaptoethanol and syringic acid were determined as 9.110-4, 2.310-4M, 1.510-4M, 3.810-7M, 1.210-4M, 4.910-4M, and 410-4M respectively. Thus L-tyrosine was by far the most effective inhibitor. Interestingly, sulfosalicylic acid behaved as an activator of LsPPO in this study.