Studies on the Regulatory Role of fra/is-Cinnamic Acid on the Activity of the Phenylalanine Ammonia-Lyase (PAL) in Suspension Cultures of Daucus carota L

Phenylalanine Ammonia-Lyase, Protein Metabolism, Regulation, /ra/js-Cinnamic Acid, Daucus carota, Suspension Culture In vivo and in vitro experiments were performed in order to study the regulatory role of transcinnamic acid and its hydroxylated derivatives (p-coumaric acid, caffeic acid) on the deamina­ tion of phenylalanine catalyzed by PAL (EC 4.3.1.5). 7>arts-cinnamic acid inhibits growth and reduces the content of soluble proteins of anthocyanin-containing carrot cells grown in suspen­ sion. There is strong evidence from the polysomal patterns and from the effect of ?ra«5-cinnamic acid on protein synthesis in vitro that protein synthesis is inhibited. The kinetic data of PAL clearly demonstrate that /ra«s-cinnamic acid inhibits the enzyme by a noncompetitive mecha­ nism. On the contrary, L-a-aminooxy-/?-phenylpropionic acid (l-AOPP), a competitive inhibitor of PAL, does not affect protein metabolism.