'M^i 





140 

 Enzymatic Activities of Ko.iic Acid-treated PPO 



The dialysate of the control sample and kojic acid-treated PPO 

 preparations showed an equivalent volume. Data listed in Table 7 show 

 that there was no significant difference (P > 0.05) in the enzyme activity 

 between the control and the kojic acid-treated PPO following dialysis 

 against phosphate buffer. The restoration of enzymatic activity was 

 attributed to the removal of kojic acid from the enzyme mixture; the 

 failure to detect any kojic acid residue following dialysis verified this 

 assumption. These results thus indirectly suggested that kojic acid did 

 not bind irreversibly toenzyme and the inhibition on PPO was reversible. 

 Such inhibitory characteristics are in contrast to that of sulfite and its 

 derivatives (Sayavedra-soto and Montgomery, 1986; Ferrer et al . , 1989b). 



Conclusion 



Kojic acid exhibited a competitive inhibition for the oxidation of 

 r*"' -^ chlorogenic acid and catechol by potato PPO and of 4-methyl catechol and 

 chlorogenic acid by apple PPO. This compound showed a mixed-type 

 inhibition for white shrimp, grass prawn, and lobster PPO when DL-DOPA and 

 catechol were used as substrates but a mixed-type and a competitive 

 inhibition for mushroom PPO when DL-DOPA and L-tyrosine were used, 

 respectively. This compound also showed a competitive inhibition on the 

 oxidation of DL-DOPA by apple and potato PPOs. The competitive inhibition 

 ; suggests that kojic acid might be a nonmetabol izable analog of the 

 substrates (DL-DOPA, chlorogenic acid, or 4-methylcatechol) . The result 

 also implies that apple, potato, and/or mushroom PPO bear the structural 



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