Substrate specifity and inhibitors of polyphenol oxidase in aspect of darkening of fresh and frozen mushrooms (Agaricus bisporus (Lange) Sing.)

Activity of mushroom polyphenol oxidase (PPO) toward 6 substrates and inhibitory effect of cysteine, 2-mercaptoethanol, benzoic acid and sodium metabisulphite were determined. The o-diphenols which appeared to be the best substrates were: catechin, DOPA (L-3,4-dihydro-xyphenylalanine) and chlorogcnic acid. Affinity of PPO crude preparation substrates to enzyme, expressed as inverse value of Michaelis constant was lower then affinity of catechol. Inhibitory effect depended on specifity of inhibitors and their concentration. Electrophoretic patterns of PPO of mushrooms reveals slow and fast moving 4 isoforms when DOPA was used as a substrate, 2 bands for catechin and chlorogenic acid while only one band showed activity toward tyrosine and p-cresol