Thus, the two substrates of this enzyme are L-arogenate and 2-oxoglutarate, whereas its two products are prephenate and L-glutamate. However, in most plant species utilizing this enzyme, the left side of the reaction is strongly favored. Therefore, glutamate is used as the amino donor to convert prephenate into arogenate.
Nomenclature
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is L-arogenate:2-oxoglutarate aminotransferase. Other names in common use include prephenate transaminase (ambiguous), PAT (ambiguous), and L-glutamate:prephenate aminotransferase. It operates in the phenylalanine and tyrosine biosynthesis pathway.
Species distribution
The gene which encodes this enzyme has recently been identified in various plant species and microorganisms, meaning that all genes in the pathway have now been identified and accounted for. This pathway occurs in many different plant species. As phenylalanine is an essential amino acid, humans (and other animals) have lost the ability to produce it themselves and must therefore obtain it from their diet. As such, the activity of this enzyme in various plant species affects the survival of animals as well. In these animals, tyrosine is synthesized from phenylalanine via the enzyme phenylalanine hydroxylase, whereas plants have their own method of tyrosine synthesis.
Function
Glutamate—prephenate aminotransferase catalyzes the reversible reaction shown below:
The enzyme catalyzes the reaction above, an important step in the synthesis of phenylalanine, tyrosine, and tryptophan. From left to right, the species involved are L-arogenate, 2-oxoglutarate, prephenate, and L-glutamate.
,
and its primary purpose is to convert prephenate into arogenate via transamination, using glutamate as the amino donor. As stated previously, the left side of the reaction is strongly favored. This is a necessary process for any organism which needs to convert arogenate into phenylalanine or tyrosine, as arogenate is an intermediate in the reactions which synthesize these amino acids, an alternative route to that involving phenylpyruvate and hydroxyphenylpyruvate. In the absence of glutamate, aspartate can act as the amino donor in the reaction without the need for a different enzyme, but this reaction proceeds more slowly. The details of the activity of this enzyme are still somewhat of a mystery.
Structure
Little is known about the structure of glutamate-prephenate aminotransferase. However, some data indicates that the enzyme may have an α2-β2 subunit structure.
Graindorge M, Giustini C, Jacomin AC, Kraut A, Curien G, Matringe M (2010). "Identification of a plant gene encoding glutamate/aspartate-prephenate aminotransferase: the last homeless enzyme of aromatic amino acids biosynthesis". FEBS Lett. 584 (20): 4357–60. doi:10.1016/j.febslet.2010.09.037. PMID20883697. S2CID13591470.
L-Tyrosine or tyrosine 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 Greek tyrós, meaning cheese, as it was first discovered in 1846 by German chemist Justus von Liebig in the protein casein from cheese. It is called tyrosyl when referred to as a functional group or side chain. While tyrosine is generally classified as a hydrophobic amino acid, it is more hydrophilic than phenylalanine. It is encoded by the codons UAC and UAU in messenger RNA.
Amino acid biosynthesis is the set of biochemical processes by which the amino acids are produced. The substrates for these processes are various compounds in the organism's diet or growth media. Not all organisms are able to synthesize all amino acids. For example, humans can synthesize 11 of the 20 standard amino acids. These 11 are called the non-essential amino acids).
Tyrosine aminotransferase is an enzyme present in the liver and catalyzes the conversion of tyrosine to 4-hydroxyphenylpyruvate.
Prephenate dehydrogenase is an enzyme found in the shikimate pathway, and helps catalyze the reaction from prephenate to tyrosine.
Arogenate dehydratase (ADT) (EC 4.2.1.91) is an enzyme that catalyzes the chemical reaction
In enzymology, a 2,5-diaminovalerate transaminase is an enzyme that catalyzes the chemical reaction
In enzymology, 4-aminobutyrate transaminase, also called GABA transaminase or 4-aminobutyrate aminotransferase, or GABA-T, is an enzyme that catalyzes the chemical reaction:
In enzymology, an aromatic-amino-acid transaminase is an enzyme that catalyzes the chemical reaction
In enzymology, an aspartate-prephenate aminotransferase is an enzyme that catalyzes the chemical reaction
In enzymology, a D-amino-acid transaminase is an enzyme that catalyzes the chemical reaction:
In enzymology, a diaminobutyrate-2-oxoglutarate transaminase is an enzyme that catalyzes the chemical reaction
In enzymology, a dihydroxyphenylalanine transaminase is an enzyme that catalyzes the chemical reaction
In enzymology, a histidinol-phosphate transaminase is an enzyme that catalyzes the chemical reaction
In enzymology, a leucine transaminase is an enzyme that catalyzes the chemical reaction
In enzymology, a tryptophan transaminase is an enzyme that catalyzes the chemical reaction
The shikimate pathway is a seven-step metabolic pathway used by bacteria, archaea, fungi, algae, some protozoans, and plants for the biosynthesis of folates and aromatic amino acids. This pathway is not found in mammals.
Phosphoserine transaminase is an enzyme with systematic name O-phospho-L-serine:2-oxoglutarate aminotransferase. This enzyme catalyses the following chemical reaction
UDP-4-amino-4,6-dideoxy-N-acetyl-alpha-D-glucosamine transaminase is an enzyme with systematic name UDP-4-amino-4,6-dideoxy-N-acetyl-alpha-D-glucosamine:2-oxoglutarate aminotransferase. This enzyme catalyses the following chemical reaction
UDP-4-amino-4,6-dideoxy-N-acetyl-beta-L-altrosamine transaminase is an enzyme with systematic name UDP-4-amino-4,6-dideoxy-N-acetyl-beta-L-altrosamine:2-oxoglutarate aminotransferase. This enzyme catalyses the following chemical reaction
Arogenic acid is an intermediate in the biosynthesis of phenylalanine and tyrosine. At physiological pH it exists as its conjugate base arogenate as the acid form is unstable.
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