Proteins are made up of long chains of building blocks called amino acids. The sequence of the amino acid is characteristic to a particular protein and this determines its function. There are twenty or more amino acids – some of which are essential some non-essential.
Essential and non-essential amino acids
‘Essential’ means that the body cannot produce the specific amino acid and has to take them in from outside sources – either through food or supplements. Non-essential amino acids can be made by the body but can also be obtained from the diet.
The essential amino acids are:
- Methionine (and its related compound cystine)
In infants histidine is also essential.
The non-essential amino acids are:
- Aspartic acid
- Glutamic acid
The body’s requirements for the amino acids in proteins increases during periods of growth – such as infancy, during pregnancy and breast feeding, during recovery from weight loss, or in healing or recovery from burns.
Amino acids are the building blocks of protein which are often the building blocks of the body. Proteins can be divided into two types:
- Structural proteins – these are found in muscle, bones, connective tissue and to a much lesser extent in cell walls.
- Functional proteins – these include hormones such as insulin and thyroid hormone, digestive enzymes, and antibodies.
Amino acids themselves are used not only in proteins but also other molecules such as neurotransmitters (chemical that transmit electrical nerve impulses in the brain). It can be seen that there are many important functions performed by amino acids.
Therapeutic uses of amino acids
We tend to think of vitamins and mineral and essential fatty acids as being the major nutritional supplements, however, amino acids can also be used to provide therapeutic benefit.
In certain diseases there may be increased demands for certain types of proteins and if these proteins are high in one particular amino acid then the requirements for that amino acid may well be increased – an perhaps not satisfied by the diet alone. In other conditions there is a disturbance in the metabolism of a particular amino acid.
Some pharmaceutical drugs can affect amino acid metabolism. For example anti-inflammatory drugs used in the treatment of arthritis affects the metabolism of tryptophan.
Below is a list of some of the ways that amino acids have been used.
- Arginine – has been shown to improve sperm count and sperm motility in some men.
- Lysine – is used particularly for recurrent cold sores and herpes infections.
- Phenylalanine – has been used in the treatment of pain and depression.
- Tryptophan – this amino acid has been more studied than the others. There is an association between the level of tryptophan in the blood and arthritis. High levels of tryptophan are also found in jaundice. It has also been used in depression, particularly if insomnia is present. Oestrogen containing oral contraceptives interfere with the normal metabolism of tryptophan (this may be because of their effect in vitamin B6 which is essential for the conversion of tryptophan to serotonin.)
- Histidine – has been used in rheumatoid arthritis – low levels of histidine has been found in the blood of those with rheumatoid arthritis
- Tyrosine – like tryptophan and phenylalanine has been used in the treatment of depression. This amino acid is essential for the synthesis of substances called catecholamines (these include dopamine and noradrenaline) and some people who are depressed have low levels of these compounds.
It is likely that more and more uses for amino acids will become evident as research progresses.
Proteins (which contain amino acids) are essential requirement in our diet. Amino acids, essential and non-essential, are needed for the body’s structural component – bones, muscle and connective tissue and for functional aspects such as hormones and other chemicals. The range of therapeutic used for which amino acids are used is still somewhat limited it is likely that the uses will expand as we learn more about the role that amino acids play in maintaining health.