ammonialyase

Ammonialyase is a term occasionally used to describe a family of enzymes that catalyze ammonia-lyase reactions, meaning they promote non-oxidative removal of ammonia from substrates such as amino acids. It is not an officially standardized name in major biochemical databases, but it is used informally to group certain lyases that perform ammonia elimination.

Known examples that fit the concept include phenylalanine ammonia-lyase (PAL), tyrosine ammonia-lyase (TAL), and histidine ammonia-lyase (HAL). PAL and TAL catalyze the removal of ammonia from phenylalanine and tyrosine to form cinnamic and p-coumaric acids, respectively, releasing NH3 in the process. HAL converts histidine to urocanate, also with ammonia release. These enzymes are typically classified as lyases (EC 4.3.x.x) and play key roles in diverse metabolic contexts: PAL and TAL are central to the plant phenylpropanoid pathway, while HAL participates in microbial histidine metabolism.

Distribution and applications vary by enzyme. PAL and TAL are widespread in plants and some microbes and are exploited in biotechnology for production of phenylpropanoid derivatives, flavors, and fragrances. HAL is found in certain bacteria and fungi and contributes to amino-acid catabolism. In research and industry, ammonia-lyase activity is of interest for synthesizing aromatic compounds and for metabolic engineering aimed at altering carbon flow toward deaminated products.

See also: phenylalanine ammonia-lyase, tyrosine ammonia-lyase, histidine ammonia-lyase.