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Alanine

life science Maturity 11-13 Next article →

Alanine is a fundamental building block used to construct proteins. In biology, it is classified as an alpha-amino acid, which means it is a monomer used in the biosynthesis of proteins.

Alanine-spin
Alanine-spin

This molecule is essential for life because it helps form the complex structures that make up living organisms. It is characterized as a non-polar, aliphatic alpha-amino acid. This description comes from its specific structure. At its center, alanine has a carbon atom. This central atom holds an amine group and a carboxylic acid group. It also carries a methyl group, which is a small side chain. This side chain makes the molecule aliphatic.

Zwitterion-Alanine
Zwitterion-Alanine

Under the chemical conditions found in biological systems, alanine exists in a specific state called a zwitterion. In this form, the amine group is protonated, meaning it carries a positive charge. At the same time, the carboxyl group is deprotonated, meaning it carries a negative charge. This internal balance of charges is a key feature of its chemical behavior. Because of its structure, the methyl side chain is considered non-reactive. This means the side chain is rarely directly involved in the actual function of a protein. Instead, alanine often serves as a stable structural component.

There are two main versions of alanine, known as isomers. These versions are mirror images of each other, much like a left and right hand. The left-handed version is called L-alanine. This is the form that is incorporated into proteins in living things. In a study of 1,150 proteins, L-alanine was found to be very common. It is second only to L-leucine in how often it occurs, making up 7.8% of the primary structure. The right-handed version is called D-alanine. While not used in human proteins, D-alanine is found in the cell walls of some bacteria, specifically in peptidoglycan. It also appears in the tissues of many molluscs and crustaceans, where it acts as an osmolyte.

Humans do not need to eat alanine to survive because it is a nonessential amino acid. This means our bodies can manufacture it ourselves through metabolic processes. One way the body produces alanine is through a two-step process called reductive amination. First, an enzyme called glutamate dehydrogenase converts ammonia, NADH, and alpha-ketoglutarate into glutamate, NAD+, and water. In the second step, an enzyme called an aminotransferase moves the amino group from the new glutamate to a molecule called pyruvate. This reaction converts the pyruvate into alanine and regenerates the alpha-ketoglutarate.

Synthesis of alanine - 1
Synthesis of alanine - 1

History shows us how scientists first understood this molecule. In 1850, a scientist named Adolph Strecker first synthesized alanine. He did this by combining ammonia and acetaldehyde with hydrogen cyanide. He named the substance "Alanin" in German. The name is related to the word "aldehyde." He used the interfix "-an-" to make the word easier to pronounce. The German ending "-in" is similar to the English ending "-ine." This discovery allowed chemists to begin studying how amino acids function in the natural world.

Alanine plays a vital role in the glucose-alanine cycle in mammals. This cycle helps manage energy and waste between the muscles and the liver. When muscles break down amino acids for fuel, they collect amino groups in the form of glutamate. Through the action of alanine aminotransferase, this glutamate is transferred to pyruvate. This creates alanine, which then travels through the bloodstream to the liver.

Synthesis of alanine - 2
Synthesis of alanine - 2

In the liver, the process reverses. The alanine is turned back into pyruvate, which the liver then uses to create glucose through gluconeogenesis. This glucose returns to the muscles to provide energy for contraction.

Beyond biology, alanine has important uses in medical science and research. In radiotherapy, alanine is used for dosimetric measurements to track radiation doses. When alanine is exposed to radiation, it undergoes deamination. This process creates stable free radicals.

Zwitterion-Alanine
Zwitterion-Alanine

Scientists can measure these radicals using a technique called electron paramagnetic resonance. This helps doctors ensure that radiation treatment is delivered accurately to patients. Additionally, researchers use a technique called alanine scanning. In this method, they mutate positions in a gene to alanine to study how proteins function. This helps scientists understand the importance of specific parts of a protein's structure.

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File:Alanine-spin.gif
Alanine-spin.gif
File:Synthesis_of_alanine_-_1.png
Synthesis_of_alanine_-_1.png
File:Synthesis_of_alanine_-_2.png
Synthesis_of_alanine_-_2.png
File:Zwitterion-Alanine.png
Zwitterion-Alanine.png
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