Everyone is familiar with the 25 amino acids which constitute proteins (protein amino acids) , 16-20 are present frequently and only 22 are coded by DNA. But their are more than 900 amino acids exist in Plants (outside proteins -Non-protein amino acids). Some are homologous members of protein aminoacids while some others are structural isomers. More that half of these amino acids are present in legume family. Many of them are toxic to animals and to nearby plants (allelopathic interactions) and thus are considered as survival mechanisms. Many sulphur containing compounds of garlic and onioncontain them. Glutathione (g-L-glutamyl-cysteinyl-glycine), a prosthetic group of some enzymes is widely distributed among higher plants. Some of the antibiotics like Polymyxins as well as toxins of Fly Agaric (a toxic mushroom) have non protein amino acids. Pantothenic acid of coenzyme A molecule consists of pantoic acid and b-alanine. In folic acid (a member of vit. B. complex), pteroic acid occurs in peptide linkage with L-glutamic acid.
These compounds are classified as
1. D-Aminoacids (protein amino acids are L-isomers) which tresent in certainantibiotics enter into protein synthesis of pathogenic microbes and produce dysfunctional proteins (this how some antibiotics work),
2. Non-alpha Amino acids having the amino group attached in any other carbon other than the a-carbon (in normal amino acids both amino and carboxyl groups are attached to same carbon-alpha carbon),
3. Derivatives of protein amino acids like DOPA (dihydroxy phenyl alanine) a precursor of dopamine, a key neurotransmitter (messenger) in the brain. (Dopa is used in the treatment of Parkinson disease),
4. New heterocylic and alicyclic aminoacids like homologues of proline, azetidine-2-carboxylic acid and pipecolic acid and cycloprapane hypoglycin A).
5. Dicarboxylic acids and amides like a-Amino adipic acid (HOOC (CH¬2)3CH (NH¬2) COOH),
6.Sulphur containing aminoacids as alliin (as in garlic and onion) and
7. Hydroxy amino acids like g-Hydroxy glutamic acid.
These non-protein amino acids act as toxins to many animals and insects which eat them and nearby plants and thus protect the plant from plant containing them from their enemies. That is why Leguminoseae is one of the largest families and contain many weeds. As legumes have nitrogen fixing bacteria in root nodules, these amino acids are a form of storing nitrogen also.
But, on a brighter side , a number of these compounds are used in medicine. They are the following.
1. Citrulline (from Citrullus)and ornithine are precursors of alkaloids. Citrulline is used for treating erectile dysfunction
2. Ornithine helps in detoxification of liver and useful in liver cirrhosis.
3. Theanine (found in tea) acts as a muscle relaxant and aid stress reduction by changing levels of neurotransmitters in brain. It in creases production of T- lymphocytes.
4. Betaine (Trimethyl glycine in beet root and wheat bran) acts as a medicine for hepatitis and artherosclerosis.
5. Taurine (milk and fish) lower cortisol levels as it controls anxiety and stress levels. It also increases athletic performance. It also prevents diabetes and reduces lipid levels. It is also needed for proper development of retina.
Source:
Useful Herbs of the Planet Earth, M. Daniel, (2012), Scientific Publishers, Jodhpur, Pages 710, and google searches.
Mammen Daniel
