36 

 ; while 37°C was reported for banana PPO using dopamine as substrate 

 (Palmer, 1963). Regarding potato and grape PPO activity, the optimum 

 temperature of 25°C was reported for the former (Lavollay et al . , 1963), 

 while lO-lS^C for the latter (Cash et al., 1976). The data available 

 indicate that the temperature optimum of the enzyme also depends 

 essentially on the same factors as the pH optimum (Vamos-Vigyazo, 1981). 

 It is noted that most crustacean PPOs had higher temperature optima than 

 those observed for plant PPOs. With the exception of banana PPO, which 

 showed an unusually high temperature optimum at 37°C (Palmer, 1963). 



Both lobster PPOs exhibited similar thermostability characteristics, 

 although the Australian lobster PPO showed decreased activity when pre- 

 incubated at temperatures greater than 30°C (Figure 6). However, Florida 

 lobster PPO showed greater stability at a preincubation temperature of 

 SS'C, which was within the range of EAPO (endogenously activated 

 phenol oxidase) and TAPOl forms but slightly different from the IPOl form 

 of the Florida spiny lobster PPO (Ferrer et al . , 1989a). The 

 thermostability characteristics of both lobster PPO's behave similarly to 

 that of grass prawn (Rolle et al., 1991) and pink shrimp PPO (20-30°C, 

 Simpson et al., 1988a) but varied from that of white shrimp PPO (25-50°C, 

 Simpson et al . , 1987). Florida spiny lobsters grew in warm water while 

 Western Australian lobsters are found in cold water. These differences in 

 their habitats may account for the difference in the optimal 

 thermostability between these two enzymes. PPO enzymes from shrimp are 

 usually stable at temperatures ranging between 30° and 50°C (Madero and 

 Finne, 1982; Simpson et al . , 1987, 1988a). Most PPO enzymes are heat 



