. . . ^ : ^ ♦ 26 



molecular weights of the proteins were determined following the methods of 

 Weber and Osborn (1969) and Weber et al . (1972). 



Enzyme Kinetics Study 



Kinetic parameters (K^ and V^^) of the two lobster PPO's were 

 determined using the Lineweaver-Burk equation (Lineweaver and Burk, 1934). 

 DL-DOPA and catechol solutions at concentrations varying from 1.67 to 9.92 

 mM in 0.05 M phosphate buffer (pH 6.5) were used as substrates. PRO 

 activity on catechol was defined as /imoles of benzoquinone formed per min 

 at 25°C. One molecule of catechol produced one molecule of benzoquinone, 

 which has a molar absorption coefficient (a^pj) of 1,350 M'^ cm'^ (Whitaker, 

 1972). 



In addition, Michael is constants (K^) for mushroom, potato, apple, 

 white shrimp, and grass prawn PPOs were determined. Sixty-^L PPG was 

 added to 10 mM DL-DOPA in 0.05 M sodium phosphate buffer (pH 6.5), The 

 total volume in the cuvette was 1.0 mL and the final concentration of DL- 

 DOPA varied from 1.4 to 8.9 mM. The reaction was monitored at 475 nm and 

 25''C for 10 min. 



Results and Discussion 



Effect of dH on Lobster PPG Activity 



PPG enzymes isolated from Western Australian lobster and Florida 

 spiny lobster exhibited similar patterns of sensitivity to pH changes. 

 Florida spiny lobster PPG had a pH optimum of 6.5, which was a half unit 

 less than that for Western Australian lobster PPG (Figure 3). These 

 values for the two lobster PPG's were similar to that of gulf (brown) 



