Arogenate dehydratase (ADT) () is an enzyme that catalyzes the chemical reaction : L-arogenate → L phenylalanine + H₂O + CO₂ Certain forms of the protein have the potential to catalyze a second reaction, :L-prephenate → L-phenylpyruvate + H₂O + CO₂ This enzyme participates in phenylalanine, tyrosine, and tryptophan biosynthesis (an example structure is shown to the right.

Nomenclature

This enzyme belongs to the family of lyases, specifically the hydro-lyases, which cleave carbon-oxygen bonds. The List of enzymes, systematic name of this enzyme class is L-arogenate hydro-lyase (decarboxylating; L-phenylalanine-forming). Other names in common use include: * arogenate dehydratase * L-arogenate hydro-lyase (decarboxylating) * cyclohexadienyl dehydratase * carbocyclohexadienyl dehydratase * pheC * ADT

Reaction

The Carboxyl group, carboxyl and Hydroxide group, hydroxide groups (shown in red) attached to the 2,5-cyclohexene ring are eliminated from L-arogenate, leaving as carbon dioxide and water. The 2,5-cyclohexene ring becomes a phenyl ring, and L-phenylalanine is formed. Certain forms of ADT have been shown to exhibit some prephenate dehydratase (PDT) activity in addition to the standard ADT activity described above. Known as cyclohexadienyl dehydratases or carbocyclohexadienyl dehydratases (listed above), these forms of the enzyme catalyze the same type of reaction (a decarboxylation and a Dehydration reaction, dehydration) on prephenate. The carboxyl and hydroxide groups (in red) attached to the 2,5-cyclohexene ring are removed, leaving phenylpyruvate. Secondary reaction catalyzed by arogenate dehydratase

Function

ADT catalyzes a reaction categorized by two major changes in the structure of the Substrate (biochemistry), substrate, these being a decarboxylation and a dehydration; the enzyme removes a carboxyl group and a water molecule (respectively). Both potential products of this reaction (L-arogenate and phenylpyruvate) occur at or near the end of the biosynthetic pathway. Total synthesis of L-arogenate has been reported.

Structure

The structure of arogenate dehydratases are described as having, for the most part, three major sections. ADTs contain an N-terminus, N-terminal transit peptide, a Prephenate dehydratase, PDT-like domain, and an ACT domain, ACT (Aspartokinase, chorismate mutase, TyrA) domain.

Homologues

Homology (biology), Homologues for ADT have been isolated in ''Arabidopsis thaliana (''rabbit-ear cress'')'', ''Nicotiana sylvestris'' (tobacco), ''Spinacia oleracea'' (spinach), ''Petunia hybrida'', ''Sorghum bicolor'', ''Oryza sativa'', and ''Pinus pinaster'' which are all considered higher-order plants. ''Erwinia herbicola'' and ''Pseudomonas aeruginosa'' are known to have homologues for cyclohexadienyl dehydratase. Of the plants with ADT homologues, both ''Arabidopsis thaliana'', ''Petunia hybrida'', and ''Pinus pinaster'' are known to have paralogues for the gene (six, three, and nine, respectively).

References

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