CONCLUSIONS 



Polyphenol oxidase (PPO) from various sources vary with respect to 

 their substrate specificity, kinetic properties, isoforms, molecular 

 weights, activation energy (EJ, isoelectric point (pi) and activity and 

 stability to pH and temperature effects. Tyrosine, phenylalanine, DOPA, 

 and tyramine have been identified as predominant phenolic substrates of 

 crustacean (lobster, crab, and shrimp) PPO. For mushroom and other plant 

 PPOs, the substrate, however, varied with the sources of enzyme. 

 Crustacean PPO had a narrow range of optimum pH between 6 to 8 compared 

 with the broad one (4 to 7) observed for mushroom and plant PPOs. 

 Regarding temperature optimum, crustacean PPOs had greater ranges than 

 plant PPOs. Using immunological techniques, plant (potato and apple), 

 mushroom, and crustacean (Florida spiny lobster, white shrimp, and brown 

 shrimp) PPOs were shown to share similar antigenic determinants. Varied 

 compositional secondary structures (a-helix, ^-sheet, ^-turn, and random 

 coil) as revealed by spectropolarimetric analysis however existed among 

 these different PPOs. 



Kojic acid was shown to inhibit PPO activity from the various 

 sources. It was a competitive inhibitor for the oxidation of chlorogenic 

 acid and catechol by potato PPO and 4-methylcatechol and chlorogenic acid 

 by apple PPO. This compound showed a mixed-type inhibition for lobster, 

 grass prawn, and white shrimp PPO when ;S-3,4-dihydroxyphenyl alanine (DOPA) 

 and catechol were used as substrates, but a mixed-type and a competitive 



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