STRUCTURAL COMPARISON OF CRUSTACEAN, PLANT, AND MUSHROOM 



POLYPHENOL OXIDASES 



Introduction 



Polyphenol oxidase (PPO) (E.C. 1.14.18.1.), also known as 

 tyrosinase, polyphenol ase, phenolase, catechol oxidase, cresolase, and 

 catecholase, is widely distributed in nature (Schwimmer, 1981). The 

 unfavorable enzymatic browning caused by PPO on the surface of many plants 

 and seafood products has been of a great concern to food processors and 

 scientists. Although the formation of melanin (blackening spot) does not 

 affect the nutrient content of food products, it does however connote 

 spoilage by consumers (Eskin et al . , 1971). Economic loss resulting from 

 this action has caused great concern among food processors. Enzymatic 

 browning of fruits, vegetables, and crustaceans due to PPO activity has 

 been extensively studied (Chen et al . , 1991a; Ferrer et al . , 1989a; 

 Flurkey and Jen, 1978; Macrae and Duggleby, 1968; Sciancalepore and ' 

 Longone, 1984; Simpson et al., 1989a; Walker, 1964). " ^ ^J ^ ' '?J ; 



Differences in the secondary structure between endogenously 

 activated (EAPO) and trypsin activated (TAPO) forms of Florida spiny 

 lobster PPO was recently demonstrated by Rolle et al . (1991) using 

 circular dichroism (CD) spectropolarimetry. A study conducted by Chen et 

 al. (1991b) showed that PPOs from plant and crustacean sources not only 

 varied with respect to catalytic activity in the oxidation of DL-;3-3,4- 

 dihydroxyphenyl alanine (DL-DOPA) but also had different sensitivities to 



52 



