Phenylalanine racemase (ATP-hydrolysing)

The enzyme phenylalanine racemase is of the enzyme category EC 5.1.1 (acting on amino acids and derivatives). It activates both the L & D stereo isomers of phenylalanine to form L-phenylalanyl adenylate and D-phenylalanyl adenylate, which are bound to the enzyme. These bound compounds are then transferred to the thiol group of the enzyme followed by conversion of its configuration, the D-isomer being the more favorable configuration of the two, with a 7 to 3 ratio between the two isomers. The racemasation reaction of phenylalanine is coupled with the highly favorable hydrolysis of adenosine triphosphate (ATP) to adenosine monophosphate (AMP) and pyrophosphate (PP), thermodynamically allowing it to proceed. This reaction is then drawn forward by further hydrolyzing PP to inorganic phosphate (Pi), via Le Chatelier's principle.

Other names

 * phenylalanine racemase
 * phenylalanine racemase (adenosine triphosphate-hydrolysing)
 * gramicidin S synthetase I

Pathway

 * Phenylalanine Metabolism

Substrate

 * L – Phenylalanine

Product

 * D - Phenylalanine

Cofactor

 * Pyridoxal-phosphate (active form of vitamin B6)

Links to disease
Problems in the digestion of phenylalanine (phe) to tyrosine (tyr) lead to the build up of both phe and phenylpyruvte, in a disease called Phenylketonuria (PKU). These two compounds build up in the blood stream and cerebral spinal fluid, which can lead to mental retardation if left untreated. Treatment consists of a restricted diet of foods that contain phe or compounds that can breakdown into phe. Children in the US are routinely tested for this at birth. For more information see the Phenylketonuria page or the link below.

Database links

 * KEGG
 * BRENDA
 * ExPASy
 * PDB

ID Numbers

 * UniProt: P14687
 * PDB: 1amu
 * ECnumber: 5.1.1.1
 * CAS: 37290-95-2

Quick facts

 * pH Range = 7.2 – 8.6
 * Equilibrium Ratio: L-Phe:D-Phe = 3:7
 * Specific Activity: 0.019

The reaction

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The pathway
The Phenylalanine Metabolism Pathway from the KEGG website. Phenylalanine Racemase Enzyme is in red.


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Links

 * Learn more about PKU at www.pku.com


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