Catalyzes the non-oxidative deamination of L-phenylalanine to form trans-cinnamic acid, the first step in the phenylpropanoid pathway. L-phenylalanine = (E)-cinnamate + NH4(+) kcat is 4.3 sec(-1) for phenylalanine (PubMed:17240984). kcat is 4.6 sec(-1) for phenylalanine (PubMed:18556022). Retains activity after 10 minutes exposure to pH values between 4 and 12 (PubMed:18556022). Optimum pH is 7.7-8.5. Phenylpropanoid metabolism; trans-cinnamate biosynthesis; trans-cinnamate from L-phenylalanine: step 1/1. Homotetramer. 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.