The reaction catalyzed by PAL is the deamination of L-phenylalanine to yield tramcinnamic
acid and amm0nia.l There are no cofactor requirements. Preparations from many
plant sources also catalyze the deamination of L-tyrosine to truns-p-coumaric acid and ammonia,
although always to a lesser extent. Tyrosine ammonia lyase (TAL) is sometimes
considered to be a separate enzyme. 7-g Phenylalanine, stereospecifically labelled with isotopic
hydrogen at C-3 has been used to establish that the pro-S proton from C-3 of Lphenylalanine,
together with ammonia, is eliminated in an antiperiplanar fashion from C-3