This is a key enzyme of plant metabolism catalyzing the first reaction in the biosynthesis from L-phenylalanine of a wide variety of natural products based on the phenylpropane skeleton. L-phenylalanine = (E)-cinnamate + NH4(+) Competitive inhibition by cinnamic acid (CA). Phenylpropanoid metabolism; trans-cinnamate biosynthesis; trans-cinnamate from L-phenylalanine: step 1/1. Homotetramer. Circadian-regulation with peak levels occurring at the end of the light period in flowers (PubMed:26124104, PubMed:12590126). Triggered by EOBI in flowers via the regulation of its promoter (PubMed:23275577). Contains an active site 4-methylidene-imidazol-5-one (MIO), which is formed autocatalytically by cyclization and dehydration of residues Ala-Ser-Gly. Belongs to the PAL/histidase family.