Phenylalanine ammonia-lyase

Phenylalanine ammonia-lyase (PAL) is an enzyme that catalyzes the deamination of phenylalanine to trans-cinnamic acid and ammonia. This reaction is the first step in the phenylpropanoid pathway, which is responsible for the biosynthesis of a variety of secondary metabolites in plants, including flavonoids, lignin, and phenolic acids.

Structure

PAL is a tetramer with four identical subunits. Each subunit contains a MIO (3,5-dihydro-5-methylidene-4H-imidazol-4-one) group, which is essential for the enzyme's catalytic activity. The MIO group is formed by the spontaneous cyclization and dehydration of a tripeptide sequence in the protein chain.

Function

The primary function of PAL is to catalyze the non-oxidative deamination of phenylalanine to trans-cinnamic acid and ammonia. This reaction is the first step in the phenylpropanoid pathway, which leads to the production of a wide variety of secondary metabolites in plants. These metabolites play important roles in plant defense against pathogens and herbivores, as well as in plant-pollinator interactions.

Role in Disease

In humans, defects in the gene encoding PAL can lead to phenylketonuria, a metabolic disorder characterized by an inability to metabolize phenylalanine. This can result in the accumulation of phenylalanine and its metabolites in the body, leading to a variety of neurological symptoms.

See Also

• Phenylpropanoid pathway
• Phenylketonuria
• Enzyme