Comparative studies on the polyphenol oxidase fraction from lobster and tyrosinase
1992
Opoku-Gyamfua, A. | Simpson, B.K. | Squires, E.J.
Polyphenol oxidase (EC 1.10.3.1) fraction was extracted from the skin layer between the muscle and the exoskeleton of lobster (Homarus americanus), and its properties were compared with those of commercial tyrosinase. The lobster PPO fraction was activated by trypsin, and its pH optimum for the oxidation of Dopa was determined as 6.5. The lobster enzyme was most stable at pH 7.5, while tyrosinase exhibited a much broader pH stability range, from 6.5 to 10.0. The temperature optimum for the oxidation of Dopa was 30 degrees C with the lobster enzyme and 40 degrees C with tyrosinase. The lobster enzyme was more heat labile as compared with commercial tyrosinase. While the lobster enzyme lost most than 50% of its original activity after 30 min of incubation at 35% C,tyrosinase retained approximately 90% of its original activity after 30 min of incubation at 55 degrees C. The activities of both enzymes were enhanced by copper but inhibited by cysteine, p-aminobenzoic acid, and EDTA.
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