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70 



Immunological Characteristics of PPQ 



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^ : The absorbance at 405 nm of a lobster PPO-antibody reaction mixture 

 in the presence of various competitors (lobster, white shrimp, brown 

 shrimp, mushroom, and potato PPG) was determined by ELISA (Figure 14). 

 The color intensity was reduced by 18 - 79% of the control (Abs. = 0.967) 

 when the various competitor-antibody mixtures containing 12.5 ng 

 competitor and 5 /xg antibody per sample well were added to the microplate. 

 The increase of the competitor up to 100 ng/well slightly reduced the 

 color intensity. For mushroom PPG, the competition with lobster PPO for 

 antibody however was not enhanced even when mushroom PPG was added at 100 

 ng/well. The result again indicated that these PPGs were partially cross- 

 reactive and therefore shared similar structural components. From the 

 extent of competition for lobster PPO-specific antibody, white shrimp and 

 brown shrimp PPO were shown to share more antigenic similarity to lobster 

 PPO than potato and mushroom PPO (in descending order). 



Complete transfer of PPO bands along with protein standards from an 

 acrylamide gel onto a nitrocellulose membrane was achieved following 

 electro-transferring; the staining of the treated gels with Coomassie blue 

 revealed no protein bands. The purified lobster, white shrimp, brown 

 shrimp, mushroom, and potato PPG had only one protein band, while crude 

 lobster PPO had 3 isozymes (Figure 15). The nitrocellulose membrane, 

 following staining with lobster PPO-specific antibody, was found to 

 contain dark bands corresponding to potato, lobster, white shrimp, and 

 brown shrimp PPO and the crude lobster PPG preparation. Three dark bands 

 were observed for both the potato PPG and the crude lobster PPO 

 preparation, while only one dark band was found for purified lobster, 



