Phenylalanine Ammonia-lyase in Sweet Potato Roots: Inhibition by Phenylpropanoids

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  • MINAMIKAWA TAKAO
    Laboratory of Biochemistry, Faculty of Agriculture, Nagoya University
  • URITANI IKUZO
    Laboratory of Biochemistry, Faculty of Agriculture, Nagoya University

Description

Mode of inhibition of some conceivable intermediates of chlorogenic acid synthesis and other related compounds on the activity of phenylalanine ammonia-lyase A and B of sweet potato roots were investigated.<br> Among the phenylproponoids examined, trans-cinnamic, p-eoumaric and caffeic acids showed competitive inhibition on phenylalanine ammonia-lyase A, and trans-cinnamic acid in-hibited competitively the activity of phenyl-alanine ammonia-lyase B. trans-Cinnamic acid which is the direct product of the deamina-tion reaction, was found to be the most potent inhibitor of the two enzymes. DL-p-Fluoro-phenylalanine and L-tyrosine were also com-petitive inhibitors in both cases. The inhibitor constants for these competitive inhibitors were calculated. Choorogenic and isochlorogenic acids, the major polyphenols accumulated in sweet potato roots, showed no inhibitory effect on the enzyme activity. Quinic acid, the non-aromatic moiety of chlorogenic acid, was not effective on the inhibitory action of the phenolic inhibitors, and quinic acid itself did not show inhibition on the enzyme activity.

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