sentences:  Furthermore, FAH does not share known protein sequence homologs with other nucleotides or amino acids.The active site of FAH contains  Ca2+ which acts to bind the substrate and a Glu-His-Water catalytic triad functions where  the imidaxole ring of His133 activates a nucleophilic water molecule to attack the carbon-carbon bond of fumarylactoacetate thus forming fumarate and acetoacetate.Similar to Phenylalanine-associated pathways, the reaction molecular basis is critical in mammalian metabolism, as evidenced by the observed liver enzyme activity in FAH deficiency during hereditary tyrosinemia type 1.