Amino acids
The basic building blocks of proteins are amino acids. They are essential for a healthy body as they play an important role as intermediates in metabolism, regulating the metabolic processes in the human body, and participating in a number of processes such as neurotransmitter transport and biosynthesis.
The first amino acid was discovered and isolated by French chemists Louis-Nicolas Vauquelin and Pierre Jean Robiquet in 1806. They isolated it from Asparagus and named the amino acid after its name as asparagine.
The term amino acid in the English language came into use from 1898. Cystine was discovered in 1810 and cysteine was discovered in 1884.
Glycine is the first amino acid to be identified and it is the simplest amino acid discovered in 1820.It is named Glycine for its sweet taste (glyco, “sugar”) and isolated from the protein gelatin.
Threonine is the last one among the 20 common amino acids, and it was discovered in 1935 by William Cumming Rose.
In 1902, Emil Fischer and Franz Hofmeister proposed that special bonds called peptide bonds join amino acids to form proteins.
During the process of digestion, proteins in the diet are broken down into amino acids in the gastro-intestinal tract and are carried through the bloodstream, to liver and other parts of the body where they are needed.
There, they are reassembled to form specific proteins required by different cells and tissues of the body.
Structurally, Amino acids can occur in two forms, L- and D. D form, Dexter, in Latin means “right”, L form, Laevo, in Latin means “left”.
Both forms are mirror images of each other and of these two forms, cells use only L-forms, only a few D-amino acids such as D-serine occur in bacterial envelopes as neuromodulators and in some antibiotics.
Amino acids are organic compounds and they contain two functional groups i.e., amine (-NH2) and carboxyl (-COOH).
Nearly 500 amino acids are known so far and they are classified in different ways.
Amino acid residues in the form of proteins, form the second-largest component (water is the largest) of human muscles and other tissues.
Based on their protein formation function, they are classified into proteinogenic ("protein-building") amino acids and non- proteinogenic amino acids.
Only 22 are proteinogenic and many are non- proteinogenic amino acids. Proteinogenic amino acids participate in protein formation function.
They are linked in varying sequences to make all different types of proteins.
The type and the sequence of amino acids in a protein are determined by genes in the form of genetic code.
Twenty of the proteinogenic amino acids are known as "standard" or “natural” amino acids as they have universal genetic code.
The remaining 2 amino acids, (selenocysteine and pyrrolysine), are combined to form proteins by unique synthetic mechanisms.
Non-proteinogenic amino acids occur as intermediates in the metabolic pathways for standard amino acids such as in the biosynthesis of the neurotransmitter, synthesis other molecules such as precursors of certain hormones like epinephrine and norepinephrine and some neurotransmitters.
Based upon their occurrence, they are classified into essential or indispensable and non- essential amino acids.
Most of the amino acids can be synthesized by our body, but 8 (10 in children) cannot be synthesised. All these eight amino acids are referred to as essential or indispensable because the human body cannot make them and must therefore be provided by the diet. Unlike fats and starch, amino acids cannot be stored in the body.
So, all essential amino acids should be supplied along with the food. Remaining amino acids can be synthesised by the body, so they are said to be non- essential amino acids.
The essential amino acids are arginine, histidine (both are required only for children/infants), isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
These amino acids are required in the diet.
Plants can make all the amino acids, but humans cannot synthesise all because of the absence of enzymes required for the biosynthesis of all amino acids.
Today, amino acids are used as one of the nutritional supplements in the field of orthomolecular medicine, to prevent and to treat disease.
Other important functions of amino acids include reduction of hair loss, better circulation, immunity, fertility, weight problems, skin problems, sleep disorders, mood swings and erectile disorders, arthritis, diabetes, cardiovascular imbalance (high cholesterol levels, high blood pressure) or even menopausal complaints.
Only amino acids are capable of forming tissues, organs, muscles, skin and hair.
Uses of Amino acids
Amino acids are also used therapeutically for nutritional and pharmaceutical purposes.
L-arginine is essential for cardiovascular health, for the treatment of diabetes, to produce keratin, to protect the hair from the damaging effects of hair colouring and bleaching and increase immune function to minimize disease-related hair loss.
L-methionine is needed for hair and joint health and to make amino acid L-cysteine, and being a major component of keratin, it helps to protect the hair follicles from stress and slows the greying of hair and hair thinning.
L-cysteine, which is also a major component of keratin, reduces the symptoms of androgenic alopecia and functions as the precursor to L-glutathione.
L-Lysine helps to repair damaged hair by stimulating collagen.
L-phenylalanine is essential to make amino acid L-tyrosine.
L-glutathione is required for anti-aging.
Glycine helps to produce collagen, and is also important for the digestive and central nervous systems,
Dihydroxy phenylalanine (l-dopa) is required to treat Parkinson disease;
Glutamine and Histidine are required to treat peptic ulcers.
Arginine, citrulline, and ornithine to treat liver diseases.
Proline, a non-essential amino acid, helps to maintain muscle tissues, and to produce collagen and cartilage.
Industrial applications of Amino acids
Amino acids are being used as components of a variety of biodegradable polymers which are used in environmentally friendly packaging materials and in medicine, used in drug delivery and the construction of prosthetic implants.
Water-soluble biodegradable polymers may have applications in disposable diapers and agriculture.
Amino acids are also used as biodegradable anti-scaling agents and as corrosion inhibitors.
Amino acid tyrosine is being developed to replace toxic phenols such as bisphenol.
Glycine, cysteine, and D and L-alanine are used as food additives
Mixtures of amino acids are used as flavour garnishes in the food industry.
The addition of amino acids, methionine and lysine will enrich the protein content of animal feed.
Derivatives of glutamate are used as surfactants in mild soaps and shampoos.
For the chemical synthesis of synthetic varieties of antibiotic penicillin such as β-lactam antibiotic, d-Phenyl glycine and d-hydroxyphenyl glycine are used as intermediates.
Amino acids aspartic acid and phenylalanine are used in the preparation of sweetener Aspartame.
Cystine is the least soluble of all the amino acids and excess cystine crystallization results in formation of calculi or “stones” in the kidney, ureter, or urinary bladder. The stones may cause intense pain, infection, and blood in the urine.
Excess excretion of cystine into the urine will result in genetic disorder known as cystinuria.
