Inhibition of Phenylalanine Ammonia-Lyase in vitro and in vivo by (1-Amino-2-phenylethyl)phosphonic Acid, the Phosphonic Analogue of Phenylalanine

Abstract The phosphonic analogue of ʟ-phenylalanine, (R)-(1-amino-2-phenylethyl)phosphonic acid (APEP), inhibits buckwheat phenylalanine ammonia-lyase (PAL) competitively with a K i value of 1.5 μM. The K i value for the (S)-enantiomer is 11.6 μM. The corresponding values for the enantiomers of the phosphonous analogue are 35 and 205 μm , respectively. APEP inhibits the light-induced synthesis of anthocyanin in hypocotyls of etiolated buckwheat seedlings and causes a specific increase in the endogenous phenylalanine concentration in buckwheat hypocotyls as well as other plant tissues. Kohlrabi seedlings develop normally in the presence of APEP, while their anthocyanin content is greatly reduced. These results indicate that APEP inhibits PAL in vivo.