31 

 Effect of dH on Lobster PPO Stability 



Enzyme stability over a broad pH range (2 - 12) revealed that PPO 

 obtained from both lobster species exhibited optimum stability at pH 7 

 (Figure 4). When PPO was pre-incubated between pH of 5 and 9, both 

 Florida spiny lobster and Western Australian lobster PPOs still retained 

 at least 60% of their relative activity when compared at pH 6.5. 

 Conformational changes at the active site due to dramatic pH changes may 

 have caused the significant decline in enzyme activity between pH 2 and 5, 

 and between 9 and 12. Similar changes were reported to occur with TAP02 

 (trypsin activated phenoloxidase) form of the Florida spiny lobster PPO 

 (Ferrer et al . , 1989a). PPO from pink shrimp (Simpson et al . , 1988a), 

 white shrimp (Simpson et al . , 1987), and grass prawn (Rolle et al . , 1991) 

 all exhibited optimal activity within the neutral to alkaline pH range (pH 

 6-8), and showed maximal stability at pH 8. 



Effect of Temperature on Lobster PPO Activity and Stability 



Both lobster PPOs showed temperature-related changes in enzyme 

 activity (Figure 5). Results obtained for this study showed that Florida 

 spiny lobster and Western Australian lobster PPO had the temperature 

 optimum at 35° and 30°C, respectively, (Figure 5). These values were lower 

 than those observed for the PPO of pink shrimp (40°C, Simpson et al., 

 1988a), white shrimp (45''C, Simpson et al . , 1987), and grass prawn (45°C, 

 Rolle et al., 1991). Compared to crustacean PPO, the activity of peach 

 PPO was found to increase from 3° to 37°C and then declined up to 45°C 

 (Vamos-Vigyazo, 1981). In apple, the enzyme reached its maximum activity 

 at 30°C when chlorogenic acid was used as substrate (Vamos-Vigyazo, 1981); 



