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Definition, Structure, Metabolism and Analysis of Amino Acids

Definition, Structure, Metabolism and Analysis of Amino Acids

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Definition of amino acids

Amino acids are the most basic substances that make up the proteins of living organisms related to life activities, and they are one of the indispensable nutrients in living organisms. Amino acids can synthesize proteins (including enzymes) or certain important nitrogenous compounds (such as nucleotides, catecholamine hormones, certain neurotransmitters, etc.), or they can be converted into sugars or fats. Some amino acids are neurotransmitters in their own right, and some can be involved in certain metabolic activities.

Amino acid structure

General formula of the structure of amino acids:

Amino acid structure

Different side chain groups have different physicochemical properties.

Protein amino acids: In protein biosynthesis, they are carried by specialized tRNA and are directly involved in protein molecules. 22 types of protein amino acids. They have the same structural formula and differ in the side chain group (R group). All organisms contain 20 common amino acids. 2 uncommon protein amino acids are selenocysteine (21st) and pyrrole lysine (22nd). Selenocysteine is found only in selenocyte-containing proteins, while pyrrole lysine is found only in some prokaryotic organisms as a component of certain enzymes related to methanogenesis.

Non-protein amino acids: Cannot be directly incorporated into protein molecules or are post-translational modification products of protein amino acids, e.g., citrulline, ornithine, and hydroxyproline.

Amino acid metabolism

The metabolism of amino acids in the body consists of two aspects. On the one hand, they are mainly used for the synthesis of proteins, peptides and other nitrogenous substances specific to the body itself. On the other hand, they can be broken down into α-keto acids, ammonia, amines and carbon dioxide by deamidation and decarboxylation. The α-keto acids produced by amino acid catabolism can be converted into sugars and lipids or re-synthesized into certain non-essential amino acids, or oxidized to carbon dioxide and water through the tricarboxylic acid cycle, and emit energy.

Schematic representation of amino acid metabolism in different cell typesSchematic representation of amino acid metabolism in different cell types (Sormendi et al, 2018)

As an important material basis for maintaining endostasis, amino acid metabolism in the human body is in dynamic equilibrium under normal conditions. However, defects in the related proteins and enzymes involved in amino acid metabolism, or in other pathological states, can lead to/be accompanied by abnormal fluctuations in amino acid levels in, for example, blood and urine.

Amino acid analysis methods

Amino acids are widely distributed in biological fluids and are involved in many biological processes such as the synthesis as proteins, fatty acids and ketone bodies. Changes in amino acid levels in living organisms have been found to be closely associated with several diseases in fluids, such as type 2 diabetes, kidney disease, liver disease and cancer. Therefore, the development of analytical methods for the determination of amino acids and the determination of their concentration in biological samples helps to study the physiological role of amino acids in relation to the prediction, diagnosis and mechanism of diseases.

The chromatography-mass spectrometry technique uses chromatography as the separation system and mass spectrometry as the detection system. The sample is separated in the mobile phase and chromatographic fraction. After ionization, the ion fragments are separated by mass number by the mass analyzer of the mass spectrometer. The mass spectra are obtained after passing through the detector. Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry (UPLC-MS/MS) technology combines the high separation power of chromatography with the structural identification advantages of mass spectrometry to achieve baseline separation of isomers, thus giving the possibility of amino acid detection with greater specificity, higher precision and wider detection range.

Creative Proteomics amino acid mass spectrometry services can be used to detect and analyze a wide range of amino acid levels in blood, urine, other biological fluids, and tissues.


  1. Sormendi, S., & Wielockx, B. (2018). Hypoxia pathway proteins as central mediators of metabolism in the tumor cells and their microenvironment. Frontiers in immunology, 9, 40.
For Research Use Only. Not for use in diagnostic procedures.

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