Aspartic Acid: Structure, Sources, and Properties

Aspartic acid is an α-amino acid that is used in the biosynthesis of proteins.

• The L-isomer of aspartic acid is one of the 22 proteinogenic amino acids or protein building blocks.
• One of two D-amino acids present in mammals is D-aspartic acid.
• Aspartic acid, like all other amino acids, has an amino group and a carboxylic acid.
• Under physiological conditions, its α-amino group is in the protonated -NH₃⁺ state, whereas its α-carboxylic acid group is deprotonated -COO^-.
• Aspartic acid contains an acidic side chain (CH₂COOH) that interacts in the body with other amino acids, enzymes, and proteins.

Key Terms: Aspartic acid, Proteins, Amino acids, α-amino group, Citric acid cycle, Krebs cycle, Molecule, Atoms, Isoelectric point, pH value

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What is Aspartic Acid?

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Aspartic acid, also known as amino succinic acid, is a natural dibasic amino acid having two carboxyl groups (one on the alpha carbon atom and another on the side chain).

• Aside from culture media, detergents, nutritional supplements, germicides, and fungicides, aspartic acid is beneficial in a variety of other applications.
• Aspartic acid is represented by Asp or D.
• Aspartic acid is essential in the Krebs cycle or citric acid cycle.
• It is involved in the building of other biological and amino acids such as asparagine, methionine, isoleucine, arginine, threonine, and lysine.

Aspartic Acid Structure

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Sources of Aspartic Acid

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Sugar cane and beet molasses are the primary sources of aspartic acid. Other food sources of aspartic acid are

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Chemical Properties of Aspartic Acid 

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Aspartic acid is an acidic polar α-amino acid that has one extra methylene group that bonds to one carboxyl group.

• Therefore, aspartic acid is a dicarboxylic amino acid.
• Because of the existence of a second carboxyl group, the molecule is very hydrophilic.
• At neutral pH, the pKa of the second carboxyl group is around 3.85, and the whole molecule is negatively charged.
• It can be found almost at the surface of proteins due to the presence of a negatively charged carboxyl group.
• The charged group can form ionic bonds with different metal ions as well as dipole interactions with water.
• This is the major concept in amino acid solubility in water.
• Aspartic acid has an isoelectric point of 2.77 due to the presence of two carboxyl groups in the molecule.
• The pKa value of a carboxyl group bonded to alpha carbon is 1.88, 3.65 for a -COOH group at the side chain, and 9.60 for an amino group.
• Half of the sum of pKa1 and pKa3 equals the isoelectric point.
• Aspartic acid's neutral form is dominant between pH 1.88 and 3.65.
• Hence the isoelectric point is halfway between these two values, i.e. 1/2 (pKa1 + pKa3), so the isoelectric point is 2.77.

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Aspartic Acid Hybridization

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The hybridization of aspartic acid is discussed below

• The IUPAC name of aspartic acid is 2-Aminobutanoic acid, and its chemical formula is HOOCCH (NH₂)CH₂COOH.
• The molecule has four carbon atoms in total.
• Two of which are carbonyl carbon atoms from the carboxyl group.
• Both carboxyl groups' carbon atoms (C₁ and C₄) are sp² hybridized with trigonal planar geometry and a bond angle of 120^o.
• C₂ and C₃ have been sp³ hybridized and are organized in tetrahedral geometry with a bond angle of 109.28^o.
• With a bond angle of 120^o, both carbonyl carbon atoms of the carboxyl group are sp² hybridized.
• The amino group's nitrogen atom is sp³ hybridized, with two hybridized orbitals connected to the s-orbital of hydrogen atoms and one sp3 hybridized orbital overlapping with the sp³ hybrid orbital of the parent chain's C₂ atom.

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Importance of Aspartic Acid

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The following are the importance of aspartic acid

• This acidic amino acid is used for treating chronic fatigue.
• Aspartic acid causes the coenzyme NADH or nicotinamide adenine dinucleotide molecules to move from the main cell body to the mitochondria.
• They are converted into adenosine triphosphate (ATP), which serves as the fuel for all cellular activity.
• Aspartic acid helps in the transfer of minerals to cells that are required for healthy RNA and DNA.
• It also helps to enhance the overall immune system by increasing the production of antibodies and immunoglobulins, which are immune system proteins.
• Aspartic acid helps in maintaining high NADH concentrations in brain cells. 
• It also increases mental sharpness, leading to the creation of more neurotransmitters and chemicals required for optimum mental functioning.
• It also helps in various metabolic activities for the elimination of excess toxins like ammonia from cells, found to be extremely harmful to the brain, neurological system, and liver.
• In situations of stress, like with other non-essential amino acids, an additional dose of aspartic acid, which is typically delivered by protein supplements promoted as energy boosters, will be useful.

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Things to Remember

• Aspartic acid is an α-amino acid that is used in the biosynthesis of proteins.
• It is an acidic polar α-amino acid that has one extra methylene group that bonds to one carboxyl group.
• The IUPAC name of aspartic acid is 2-Aminobutanoic acid.
• Its chemical formula is HOOCCH (NH₂)CH₂COOH.
• Aspartic acid, like all other amino acids, has an amino group and a carboxylic acid.
• Aspartic acid is also known as amino succinic acid.

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