Besides the post-translationally cyclizing catalytic Ala-Ser-Gly triad, Tyr110 and its equivalents are of the most conserved residues in the active site of phenylalanine ammonia-lyase (PAL, EC ), histidine ammonia-lyase (HAL, EC ) and other related enzymes. The Tyr110Phe muta-tion results in the most pronounced inactivation of PAL indicating the importance of this residue.