;*;i'ij' 



m 



white shrimp, and brown shrimp PPO (Figure 16). Incomplete protein 

 transfer or torsional changes in protein structure following electro- 

 transfer process was possibly responsible for the failure of mushroom PPO 

 that not to form a dark band with lobster PPO-antibody. Result from this 

 study did not support the competitive ELISA experiment obtained for 

 mushroom PPO. However, our previous findings that PPO from potato and 

 crustacean sources shared similar structural components was further 

 demonstrated. 



Spectropolarimetric Analysis of PPO ''^^'::j': 



Lobster, white shrimp, and brown shrimp PPO had similar circular 

 dichroic spectra (Figures 19, 20, and 21), which were different from those 

 of mushroom and potato (Figures 17 and 18). They all varied in their 

 secondary structures (a-helix, ^-sheet, ^-turn, and random coil) (Table 

 3). For example, white shrimp PPO had a higher percentage of 

 a-helix than brown shrimp PPO; they both showed the same broad negative 

 ellipticity between 207 and 220 nm. The percentage of a-helix of 

 mushroom, potato, and crustacean PPOs estimated using the SSE program were 

 close to the values that calculated according to the formula of Greenfield 

 and Fasman (1969). The crustacean PPO, in general, had a higher 

 percentage of a-helix and lower percentage of ^-turn than mushroom and 

 potato PPO (Table 3). The percentages of the secondary strucutures of 

 these PPO estimated from the SSE program may not represent the absolute 

 values. However, the results from this study showed that PPO from various 

 sources possessed varied secondary structures, with the crustacean sources 

 producing PPO which showed wery similar secondary structure. 



