The key difference between L-phenylalanine and DL-phenylalanine is that L-phenylalanine is the L isomer of phenylalanine whereas DL-phenylalanine is the racemic mixture of D and L isomers phenylalanine.
Phenylalanine is an essential alpha-amino acid. It has the chemical formula C9H11NO2. When considering the structure of phenylalanine molecule, it has a benzene ring (phenyl group) substituted with the methyl derivative of alanine group. Thus, this is the reason for naming it as phenyl-alanine.
CONTENTS
1. Overview and Key Difference
2. What is L-phenylalanine
3. What is DL-phenylalanine
4. Side by Side Comparison – L-phenylalanine vs DL-phenylalanine in Tabular Form
5. Summary
What is L-Phenylalanine?
L-phenylalanine is the L-isomer of phenylalanine. Phenylalanine is an alpha-amino acid having a benzene ring substituted to a methyl derivative of alanine group. This amino acid is a neutral and nonpolar compound because it is inert and hydrophobic in its benzyl side chain. The L isomer of phenylalanine is useful in the formation of proteins that are biochemically coded by DNA.
Figure 01: Structure of L-phenylalanine
L-phenylalanine is the common and stable isomer in nature. Naturally, we can find this amino acid in the breast milk of mammals. Moreover, it is useful in the manufacture of food and drinks to be sold as nutritional supplements due to its analgesic properties and antidepressant effects. The common sources of L-phenylalanine include eggs, chicken, liver, beef, milk, and soybeans.
Biologically, L-phenylalanine undergoes conversion to form L-tyrosine. L-tyrosine is also an amino acid that is coded by DNA. Furthermore, L-tyrosine converts into L-DOPA, which is responsible for the formation of dopamine, adrenaline and noradrenaline. Moreover, in plants, L-phenylalanine is important as the starting compound for the synthesis of flavonoids. Generally, L-phenylalanine is manufactured for medical, feed, and nutritional applications. The quantity of this production has been increased largely using E.coli.
What is DL-Phenylalanine
DL-phenylalanine is a racemic mixture of D and L isomers of phenylalanine. Among these two isomers, L-phenylalanine is the common and stable isomer while D-phenylalanine is uncommon due to less stable nature. However, we can produce the D-phenylalanine molecule via conventional organic synthesis. But this reaction gives the isomer as either the single enantiomer or as a racemic mixture that we can name as DL-phenylalanine. This racemic mixture cannot participate in protein biosynthesis. This type of mixtures also occurs in trace amounts in proteins.
Figure 02: Biosynthesis of Dopamine starting from Phenylalanine
We can find the DL-phenylalanine mixture in the market as a nutritional supplement. This supplement is important due to its analgesic and antidepressant properties. These properties arise due to the possible blockage of enkephalin degradation by D-phenylalanine.
What is the Difference Between L-phenylalanine and DL-phenylalanine?
Phenylalanine is an essential alpha amino acid that occurs in two isomers as the L isomer and D isomer. The key difference between L-phenylalanine and DL-phenylalanine is that L-phenylalanine is the L isomer of phenylalanine whereas DL-phenylalanine is the racemic mixture of D and L isomers phenylalanine.
Moreover, L-phenylalanine is common and stable in nature while DL-phenylalanine can be found in trace amounts. L-phenylalanine biologically converts into L-tyrosine for the formation of dopamine, can pass through the blood-brain barrier, an antagonist, can inhibit neurotransmitters, etc. DL-phenylalanine, on the other hand, has analgesic and antidepressant properties, cannot pass through the blood-brain barrier and is important as a nutritional supplement.
Below infographic tabulates in detail the differences between L-phenylalanine and DL-phenylalanine.
Summary – L-phenylalanine vs DL-phenylalanine
Phenylalanine is an essential alpha-amino acid that occurs in two isomers as the L isomer and D isomer. The key difference between L-phenylalanine and DL-phenylalanine is that L-phenylalanine is the L isomer of phenylalanine whereas DL-phenylalanine is the racemic mixture of D and L isomers phenylalanine.
Reference:
1. “DL-Phenylalanine.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine, Available here.
Image Courtesy:
1. “L-Phenylalanin – L-Phenylalanine” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia
2. “Catecholamine and trace amine biosynthesis” By Seppi333 – Own work (CC BY-SA 3.0) via Commons Wikimedia