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

The phosphonic analogue of L-phenylalanine, (/?)-(l-am ino-2-phenylethyl)phosphonic acid (A P E P ), inhibits buckwheat phenylalanine ammonia-lyase (PAL) com petitively with a K t value o f 1.5 |iM. The K, value for the (S)-enantiomer is 11.6 jj,M. The corresponding values for the enantiom ers of the phosphonous analogue are 35 and 205 |u.m , respectively. APEP inhibits the light-induced synthesis o f 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 o f A PE P, while their anthocyanin content is greatly reduced. These results indicate that APEP inhibits PAL in vivo.