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Amino acids and their analogs are found in many biotechnology, pharmaceutical, food and chemical sectors. Amino acids, the constituents of proteins, are physiologically vital components of organisms and used extensively in industry. These natural amino acids, including lysine, glutamic acid, and leucine, are naturally produced for application as food additives, feed supplements and flavour enhancers for the purpose of nutrition and taste. Furthermore, amino acid esters and salts are widely used in polymer synthesis, pharmaceutical intermediates and functional chemicals. Amide derivatives also appear in medical therapies, including antibiotics, anticancer drugs, immunomodulators and neuroprotectants. With complex structures and biological properties, they are integral to the pharmaceutical industry. Recently, advancements in biotechnology have increased the use of non-natural amino acids, which are widely applied in genetic engineering, protein engineering, and biopharmaceutical manufacturing to enhance the stability and specificity of protein drugs.
Amino acids are organic molecules, made of two functional groups, one amino (-NH2) and one carboxyl (-COOH). They are the building blocks of proteins in organisms. Amino acids are attached together by peptides into polypeptide chains, which fold back into active proteins. This is the general formula of amino acids: NH2-CHR-COOH, where R is the side chain which determines the property of the amino acid. Amino acids aren’t just the components of proteins but they are essential to many physiological processes in the body including metabolism, immune function, and neurotransmission. There are 20 natural amino acids, used in protein production, DNA genes and almost all biochemical reactions. There are also several un-standard amino acids that all serve different biological roles in different species.
The structure of amino acids consists of an amino group, a carboxyl group, a hydrogen atom, and a side chain group. The amino and carboxyl groups are located at opposite ends of the amino acid molecule, and they form the basis for amino acids to participate in protein synthesis. The hydrogen atom is attached to the carbon atom adjacent to the carboxyl group and is an indispensable part of the amino acid structure. The side chain group distinguishes each amino acid and determines its chemical properties and function in proteins. Different amino acids have different side chain groups, allowing them to form proteins with specific functions. The carbon atom directly connected to the carboxyl group is known as the α-carbon atom. With the exception of proline, the hydrogen atom on the α-carbon of the 20 amino acids that make up proteins is replaced by an amino group, making them α-amino acids. Among the 20 standard amino acids, except for glycine, the α-carbon of the other amino acids is a chiral carbon atom, existing as L- and D- isomers, but the amino acids in proteins are generally in the L-form.
Amino acids are not only the fundamental building blocks of proteins in living organisms, but they also participate in various vital physiological processes that directly influence health, metabolism, and immune function. The following are the main benefits of amino acids:
Based on the side chain groups, the 20 standard amino acids can be classified into aliphatic amino acids, aromatic amino acids, and heterocyclic amino acids. Based on the acidic or basic nature of the side chain group, they can be categorized as acidic, neutral, or basic amino acids. Based on the polarity and charge characteristics of the side chain groups, they can be divided into nonpolar amino acids, polar neutral amino acids, polar positively charged amino acids, and polar negatively charged amino acids.
Non-essential amino acids are those that the human body can synthesize through metabolic pathways. They are typically derived from other amino acids or precursor molecules. Non-essential amino acids are also critical for maintaining basic physiological functions. Examples include glycine, alanine, aspartic acid, and glutamic acid. While these amino acids do not need to be obtained from the diet, there may be increased demand during certain physiological conditions.
Hydrophobic amino acids are those whose side chains consist of nonpolar compounds, making them hydrophobic. They tend to cluster together in aqueous environments to avoid contact with water molecules. Common hydrophobic amino acids include alanine, leucine, phenylalanine, isoleucine, and valine. These amino acids are often found in the interior of proteins, helping them fold into stable three-dimensional structures. In the body, they play important roles in fat metabolism, the synthesis of endocrine hormones, and the maintenance of cell membrane structure.
Aromatic amino acids are amino acids with aromatic ring structures, mainly including phenylalanine, tyrosine and tryptophan. They have unique chemical properties and biological functions, and are essential to the structure and function of proteins. In addition, aromatic amino acid derivatives have a wide range of applications in medicine, nutrition and biotechnology, especially in drug synthesis, antioxidant research and disease treatment.
Essential amino acids cannot be synthesized by the human body and must be obtained through the diet. These amino acids are vital for normal growth, development, and metabolism. There are 9 essential amino acids for adults, including leucine, isoleucine, valine, tryptophan, phenylalanine, methionine, lysine, threonine, and histidine. These amino acids are typically abundant in animal-based proteins, particularly in meat, fish, eggs, and dairy products.
Hydrophilic amino acids have side chains with polar or charged groups that can form hydrogen bonds or ionic bonds with water molecules. Therefore, they tend to be exposed on the exterior in aqueous environments. Common hydrophilic amino acids include serine, aspartic acid, glutamic acid, and tyrosine. These amino acids are typically located on the surface of proteins, where they interact with other molecules or ions in aqueous solutions, playing essential roles in cellular signaling, enzyme catalysis, and the formation of cell membranes.
BCAAs include leucine, isoleucine, and valine. Their defining feature is the branched structure of their side chains, distinguishing them from other amino acids in terms of chemical structure. BCAAs play a significant role in muscle protein synthesis, particularly in promoting muscle repair and reducing muscle breakdown post-exercise. They bypass the liver in metabolism and are directly utilized by muscle tissue to provide energy, making them widely used in sports nutrition.
Amino acids are not only vital components of life but also play an indispensable role in various industrial fields. With their unique chemical structures, amino acids are significant in numerous industrial applications, particularly in chemical manufacturing, pharmaceuticals, food, agriculture, and materials science. As technology advances, the industrial use of amino acids is driving progress in these sectors and promoting the emergence of new industry models and innovative technologies.
In the food industry, the applications of amino acids and their derivatives are extensive. First, amino acids are essential nutrients for the human body, and many are used as food additives to meet nutritional needs. For example, L-glutamic acid, a common flavor enhancer, is widely used in various foods to enhance umami and improve overall taste. Additionally, L-lysine is often used to balance the amino acid profile of plant-based foods, enhancing their nutritional value. In sports nutrition, BCAAs are commonly added to protein supplements to aid in muscle synthesis and repair, catering to the specific needs of fitness enthusiasts. Amino acid derivatives are also used to improve food texture and flavor, with L-alanine and L-aspartic acid having notable effects on modulating sweetness and sourness. Furthermore, certain amino acid salts possess natural antimicrobial properties, making them useful in food preservation to extend shelf life and prevent microbial growth, ensuring the safety and stability of food products.
In the pharmaceutical industry, the applications of amino acids and their derivatives are multifaceted and deep. Firstly, amino acids are important raw materials in drug synthesis, with many drugs involving the use of amino acids or their derivatives. For example, amino acid derivatives such as L-alanine and L-phenylalanine are used in the synthesis of antibiotics, which play a crucial role in treating infections. With the continuous development of biotechnology, amino acids have also become an essential component of biopharmaceuticals. Amino acids not only serve as building blocks for protein-based drugs but also play a fundamental role in the production of recombinant proteins. For instance, the production of drugs such as insulin and follicle-stimulating hormone relies on the role of amino acids in protein synthesis. Additionally, amino acid derivatives play an important role in drug delivery systems. By combining amino acid derivatives with drug carriers, the bioavailability of drugs can be improved, their release rate controlled, and their stability increased. For example, the combination of PEG (polyethylene glycol) and amino acid derivatives can lead to the development of liposomes and nanoparticles with excellent performance in drug delivery, effectively enhancing targeted therapy.
In the cosmetic industry, the applications of amino acids and their derivatives are primarily seen in the manufacturing of skin and hair care products. Amino acids have excellent biocompatibility and hydrophilicity, helping to repair the skin barrier and enhance skin hydration. For example, amino acid derivatives such as glycine, glutamic acid, and alanine are commonly used in moisturizers, cleansers, and face masks. They provide deep hydration to the skin, improving its texture and elasticity. Amino acids also have antioxidant properties, which help reduce damage caused by free radicals and delay the aging process. Furthermore, amino acids play an important role in hair care products, particularly in repairing damaged hair, increasing hair shine, and softness. Many shampoos and conditioners contain amino acid-based ingredients to help restore damaged hair strands and improve hair health. The application of amino acid derivatives in cosmetics not only enhances the functionality of products but also makes them milder and non-irritating, suitable for all skin types, especially sensitive skin.
In the agricultural industry, amino acids and their derivatives contribute to sustainable agricultural production. One important application is in amino acid fertilizers, which provide essential nitrogen sources for plant growth and improve soil quality, enhancing crop growth rate and yield. Amino acid fertilizers not only improve crop resistance to stress, such as drought and disease resistance, but also increase the plant's ability to adapt to environmental changes. On the other hand, amino acid derivatives are widely used in animal feed as nutritional supplements to promote healthy growth in animals. For example, amino acid derivatives like L-lysine and L-arginine are commonly added to animal feed to enhance protein synthesis, boost immunity, and improve growth efficiency. Amino acid derivatives also act as plant growth regulators, enhancing plant disease resistance and stress tolerance. Amino acids like L-glutamic acid and L-aspartic acid effectively promote plant growth and improve crop performance under adverse conditions, thus enhancing the sustainability of agricultural production.
In the biotechnology sector, amino acids and their derivatives are widely used in bioengineering, cell culture, and biosynthesis processes. Amino acids are core components of cell culture media and are extensively used in biopharmaceutical and vaccine production. During cell culture, amino acids provide the basic nutrition needed for cell growth, promoting cell proliferation and protein synthesis. In recombinant protein production, amino acids are not only the building blocks for protein synthesis but also influence the quality and yield of recombinant proteins. Moreover, amino acids and their derivatives have extensive applications in genetic engineering. By regulating amino acid biosynthetic pathways, the microbial fermentation process can be optimized to increase product yields. In gene editing technologies, amino acid derivatives are also used as cofactors to optimize editing efficiency and advance the development of genetic engineering.
In the supplement industry, amino acids and their derivatives play an important role, particularly in sports and elderly nutrition supplementation. Amino acids, as essential nutritional components, are widely used in protein powders, amino acid drinks, and other products. These supplements not only promote muscle repair and growth but also enhance physical strength and endurance. BCAAs and arginine derivatives, in particular, have significant effects on improving exercise performance, reducing post-exercise fatigue, and preventing muscle breakdown. Furthermore, amino acids are also vital in elderly nutrition, with derivatives such as L-glutamic acid and L-aspartic acid helping maintain nervous system health, boost immunity, prevent muscle loss, and improve overall health in the elderly.
The substituent functional groups of amino acids refer to specific chemical groups in the side chains of amino acids that can influence their properties and functions through chemical modifications or changes. These substituent groups are typically formed by reactions such as acylation, methylation, or phosphorylation, which alter the polarity, hydrophilicity, or charge of the amino acid. For example, the hydroxyl group (OH) of serine can be replaced by a phosphate group (PO₄) to form phosphorylated serine, which plays a crucial role in cell signaling and protein function regulation. Similarly, amino or carboxyl groups in certain amino acid side chains can react with other molecules, altering protein structure or biological activity. Moreover, amino acids with modified functional groups have broad applications in pharmaceuticals, food, cosmetics, and materials science to improve bioactivity, enhance stability, and increase functionality and targeting.
