Arogenate dehydratase (ADT) () is an

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different molecule ...

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 Phenylalanine (symbol Phe or F) is an essential α-amino acid with the formula . It can be viewed as a benzyl group substituted for the methyl group of alanine, or a phenyl group in place of a terminal hydrogen of alanine. This essential amino a ...

tyrosine -Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group. The word "tyrosine" is from the Gr ...

, and

tryptophan Tryptophan (symbol Trp or W) is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α-amino group, an α-carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromati ...

biosynthesis (an example structure is shown to the right.

Nomenclature

This enzyme belongs to the family of

lyases In biochemistry, a lyase is an enzyme that catalyzes the breaking (an elimination reaction) of various chemical bonds by means other than hydrolysis (a substitution reaction) and oxidation, often forming a new double bond or a new ring structure. ...

, specifically the hydro-lyases, which cleave carbon-oxygen bonds. The

systematic name A systematic name is a name given in a systematic way to one unique group, organism, object or chemical substance, out of a specific population or collection. Systematic names are usually part of a nomenclature. A semisystematic name or semitrivial ...

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 In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxyl ...

and

hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water ...

groups (shown in red) attached to the 2,5-cyclohexene ring are eliminated from L-arogenate, leaving as

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...

and

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...

. The 2,5-cyclohexene ring becomes a

phenyl ring In organic chemistry, the phenyl group, or phenyl ring, is a cyclic group of atoms with the formula C6 H5, and is often represented by the symbol Ph. Phenyl group is closely related to benzene and can be viewed as a benzene ring, minus a hydrogen ...

, and L-phenylalanine is formed. Certain forms of ADT have been shown to exhibit some

prephenate dehydratase The enzyme prephenate dehydratase () catalyzes the chemical reaction :prephenate \rightleftharpoons phenylpyruvate + H2O + CO2 This enzyme belongs to the family of lyases, specifically the hydro-lyases, which cleave carbon-oxygen bonds. The s ...

(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 Decarboxylation is a chemical reaction that removes a carboxyl group and releases carbon dioxide (CO2). Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is ...

and a

dehydration In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mi ...

) on

prephenate Prephenic acid, commonly also known by its anionic form prephenate, is an intermediate in the biosynthesis of the aromatic amino acids phenylalanine and tyrosine, as well as of a large number of secondary metabolites of the shikimate pathway. ...

. The carboxyl and hydroxide groups (in red) attached to the 2,5-cyclohexene ring are removed, leaving

phenylpyruvate Phenylpyruvic acid is the organic compound with the formula C6H5CH2C(O)CO2H. It is a keto acid. Occurrence and properties The compound exists in equilibrium with its E- and Z-enol tautomers. It is a product from the oxidative deamination of p ...

Secondary reaction catalyzed by arogenate dehydratase

Function

ADT catalyzes a reaction categorized by two major changes in the structure of the

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (locomotion), the surface over which an organism lo ...

, these being a

and a

; the enzyme removes a

carboxyl group In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...

and a

water molecule Water () is a polar inorganic compound that is at room temperature a tasteless and odorless liquid, which is nearly colorless apart from an inherent hint of blue. It is by far the most studied chemical compound and is described as the "unive ...

(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-terminal The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or amine-terminus) is the start of a protein or polypeptide, referring to the free amine group (-NH2) located at the end of a polypeptide. Within a peptide, the amin ...

transit peptide A signal peptide (sometimes referred to as signal sequence, targeting signal, localization signal, localization sequence, transit peptide, leader sequence or leader peptide) is a short peptide (usually 16-30 amino acids long) present at the N-ter ...

, a PDT-like domain, and an ACT (Aspartokinase, chorismate mutase, TyrA) domain.

Homologues

Homologues for ADT have been isolated in ''

Arabidopsis thaliana ''Arabidopsis thaliana'', the thale cress, mouse-ear cress or arabidopsis, is a small flowering plant native to Eurasia and Africa. ''A. thaliana'' is considered a weed; it is found along the shoulders of roads and in disturbed land. A winter ...

(''rabbit-ear cress'')'', ''

Nicotiana sylvestris ''Nicotiana sylvestris'' is a species of flowering plant in the nightshade family Solanaceae, known by the common names woodland tobacco, flowering tobacco, and South American tobacco. It is a biennial or short-lived perennial plant in the tobacc ...

'' (tobacco), ''

Spinacia oleracea Spinach (''Spinacia oleracea'') is a leafy green flowering plant native to central and western Asia. It is of the order Caryophyllales, family Amaranthaceae, subfamily Chenopodioideae. Its leaves are a common edible vegetable consumed either f ...

'' (spinach), ''Petunia hybrida'', ''

Sorghum bicolor ''Sorghum bicolor'', commonly called sorghum () and also known as great millet, broomcorn, guinea corn, durra, imphee, jowar, or milo, is a grass species cultivated for its grain, which is used for food for humans, animal feed, and ethanol produ ...

'', ''

Oryza sativa ''Oryza sativa'', commonly known as Asian rice or indica rice, is the plant species most commonly referred to in English as ''rice''. It is the type of farmed rice whose cultivars are most common globally, and was first domesticated in the Yan ...

'', and ''

Pinus pinaster ''Pinus pinaster'', the maritime pine or cluster pine, is a pine native to the south Atlantic Europe region and parts of the western Mediterranean. It is a hard, fast growing pine bearing small seeds with large wings. Description ''Pinus pinas ...

'' which are all considered higher-order plants. ''Erwinia herbicola'' and ''

Pseudomonas aeruginosa ''Pseudomonas aeruginosa'' is a common encapsulated, gram-negative, aerobic– facultatively anaerobic, rod-shaped bacterium that can cause disease in plants and animals, including humans. A species of considerable medical importance, ''P. aer ...

'' 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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