51 

 substrate of peach (Luh and Phithakpol, 1972). Results from this study 

 show that DOPA was the unanimous substrate of crustacean PPOs. For 

 mushroom and other plant PPOs, the specific substrate varied with the 

 sources of enzyme. Mason (1955) reported that tyrosine and DOPA were 

 specific substrates of animal tissue PPO, while Mayer and Harel (1979) 

 listed a wide variety of mono- and o-diphenols as the substrates of fungal 

 and plant PPOs. Besides the previously discussed characteristics 

 (substrate specificity, K^, pH and temperature effects, enzyme isoforms, 

 and molecular weights), other biochemical properties concerning the 

 catalytical function (mechanism), response to the activator/inhibitor, and 

 isoelectric profile (pi) of PPO also varied with the enzyme sources. 



Conclusion 



PPO isolated from Florida spiny lobster and Western Australian 

 lobster showed very similar patterns in response to effects of pH and 

 temperature on enzyme activity and in SDS-PAGE profile. Using DL-DOPA and 

 catechol as substrates, the Western Australian lobster PPO was shown to 

 have higher affinity but lower physiological efficiency than the Florida 

 spiny lobster PPO. These two PPOs showed distinctly different properties 

 for catalyzing the oxidation of phenolic substrates; this may explain 

 differences in susceptibility of spiny lobster to melanosis compared to 

 Western Australian lobster. Results indicate that PPO from various plant 

 and crustacean sources vary in substrate specificity, kinetic properties, 

 molecular weights, isoforms, activity and stability to pH and temperature 

 effects, activation energy, and isoelectric profiles. 



