

I V 



100 

 L-tyrosine or 5 mM DL-DOPA in 0.05 M sodium acetate buffer (pH 6.8). The 

 reaction was monitored at 475 nm and 25°C. The potato PPO system contained 

 0.9 mL of kojic acid (20 - 800 iig/ml), 0.1 mL of enzyme, and 2.0 mL 1.4 mM 

 chlorogenic acid or 5 mM catechol in 1.0 mM sodium phosphate buffer (pH 

 7.0). The reaction was monitored at 395 nm and 25°C. The apple PPO system 

 contained 1.15 mL of kojic acid (0.02 - 2.0 mg/mL), 0.1 mL enzyme, and 2.0 

 mL of 1.4 mM chlorogenic acid or 5 mM 4-methyl catechol in 0.1 M sodium 

 phosphate buffer (pH 6.0). The reaction was monitored at 395 nm and 30°C. 

 White shrimp PPO system contained 0.45 mL of kojic acid (20 - 200 

 /ig/mL), 50 /xL of enzyme, and 1.0 mL of 5 mM L-DOPA or catechol in 0.05 M 

 sodium phosphate buffer (pH 6.5). The reaction was monitored at 40°C and 

 at 395 and 475 nm, respectively, for catechol and L-DOPA oxidation. Grass 

 prawn and lobster PPO systems contained 0.9 mL of kojic acid (20 - 150 

 /xg/mL), 0.1 mL of enzyme, and 2.0 mL of 5 mM DL-DOPA or catechol in 

 0.05 M sodium phosphate buffer (pH 6.5). The reaction was monitored at 

 25°C and 395 and 475 nm, respectively. 



Enzyme Kinetics Study 



Michael is constants, K^, for the various mushroom, plant, and 

 crustacean PPOs were determined using the Lineweaver-Burk equation 

 (Lineweaver and Burk, 1934). The substrates used for mushroom PPO, potato 

 PPO (10,900 units/mg of protein), and apple PPO (97,400 units/mg of 

 protein) were DL-DOPA (0.30 - 3.33 mM) or L-tyrosine (13.8 - 153 /xM) in 

 0.05 M sodium acetate buffer (pH 6.8), chlorogenic acid (0.60 - 6.67 mM) 

 or catechol (0.90 - 10.0 mM) in 1 mM sodium phosphate buffer (pH 7.0), and 

 4-Methyl catechol (1.0 - 9.5 mM) or chlorogenic acid (1.0 - 7.0 mM) in 





