| Type: | Active_site | Name: | Phenylalanine/histidine ammonia-lyases, active site |
| Description: | This entry represents the active site of phenylalanine ammonia-lyase (PAL; ) and the mechanistically related protein histidine ammonia lyase (HAL; ). Both contain a catalytic Ala-Ser-Gly triad that is post-translationally cyclised []. PAL is a key biosynthetic catalyst in phenylpropanoid assembly in plants and fungi, and is involved in the biosynthesis of a wide variety of secondary metabolites such as flavanoids, furanocoumarin phytoalexins and cell wall components. These compounds are important for normal growth and in responses to environmental stress. PAL catalyses the removal of an ammonia group from phenylalanine to form trans-cinnamate. HAL catalyses the first step in histidine degradation, the removal of an ammonia group from histidine to produce urocanic acid. The core domain in PAL and Hal share about 30% sequence identity, with PAL containing an additional approximately 160 residues extending from the common fold [].The two types of enzymes are functionally and structurally related []. They are the only enzymes which are known to have the modified amino acid dehydro-alanine (DHA) in their active site. A serine residue has been shown [, , ] to be the precursor of this essential electrophilic moiety. The region around the active site serine is well conserved and has been used as the signature pattern for this entry. | Short Name: | Phe/His_NH3-lyase_AS |
