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Journal of Medicinal Plants Research Vol. 5(17), pp. 3997-4000, 9 September, 2011Available online at http://www.academicjournals.org/JMPRISSN 1996-0875 2011 Academic Journals

Review

Amino acids: A review articleM. Akram1,4*, H. M. Asif2, M. Uzair3, Naveed Akhtar2, Asadullah Madni2, S. M. Ali Shah2,

Zahoor ul Hasan1and Asmat Ullah1

1Shifa ul Mulk Memorial Hospital, Hamdard University, Karachi, Pakistan.

2Faculty of Pharmacy and Alternative Medicine, The Islamia University of Bahawalpur, Pakistan.

3Faculty of Pharmacy, Bahauddin Zakariya University, Multan, Pakistan.

4Department of Basic Medical Sciences, Faculty of Eastern Medicine, Hamdard University, Karachi, Madinat-al-Hikmah,

Muhammad Bin Qasim Avenue, Karachi, Pakistan-74600, Pakistan.

Accepted 8 April, 2011

Amino acids are building blocks of protein. More than 300 amino acids have been described, but only20 amino acids take part in protein synthesis. All twenty amino acids did not appear simultaneously innature. Instead some of them appeared early, while others were added into the genetic code later. It isnecessary to take them in the diet because their deficiency results in decrease formation of protein thatultimately leads to disease condition. In this article, amino acids, its functions and associated diseaseshave been elaborated.

Key words:Amino acids, activity,diseases.

INTRODUCTION

Amino acids are basic unit of protein. Amino acidscontain an amino group and a carboxylic group. Amino

acids play major role in regulating multiple processesrelated to gene expression, including modulation of thefunction of the proteins that mediate messenger RNA(mRNA) translation (Scot et al., 2006). Amino acids areutilized in formation of protein. If amino acids aredeficient, then protein synthesis does not occur. As aresult protein deficiency disease may occur. It isnecessary to take balanced diet containing all essentialamino acids. Specific amino acids are known to acutelyand chronically regulate insulin secretion from pancreatic-cells in vivoand in vitro (Lorraine et al., 2006). Aminoacids are categorized as acidic, basic and neutral aminoacids. Some amino acids are not synthesized in the body

and it is necessary to take them in diet. Such types ofamino acids are called essential amino acids. Someamino acids are synthesized in the body and there is noneeds to take them in diet, such type of amino acids arecalled non essential amino acids. Some amino acids aresynthesized in the body but their production is insufficientsuch type of amino acids are called semi-essential amino

*Corresponding author. E-mail: makram_0451@hotmail.com.Tel: 92-021-6440083. Fax: 92-021-6440079.

acids (Hellwinkel, 2001; IUPAC-IUB, 1968). Amino acidshelp in tissue protein formation. Some amino acids are

involved in enzyme formation. Hormones like insulingrowth hormone and glucagon are made up of aminoacids. Adrenaline, nor-adrenaline and thyroxin are madeup of single amino acid. Glutathione, a physiologicallyactive peptide is also made up of amino acids. Aminoacids are involved in synthesis of melanin. It has beenstudied that amino-acid balance in cancer patients oftendiffers from that in healthy individuals, because ofmetabolic changes (Jun et al., 2010). In liver cirrhosisfunctions of dendritic cells (DCs) are impaired andcirrhotic patients may show decreased levels of plasmabranched-chain amino acids (Eiji et al., 2007).

Glutamic acid

It is an acidic amino acid. It helps in synthesis oglutathione. It is converted to alpha ketoglutaric acid intransamination reactions.

GABA

It is called gamma amino butyric acid. It is formed fromglutamic acid. It is a neurotransmitter.

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Tyrosine

Tyrosine is usually used in synthesis of thyroidhormones. It is also utilized to formDihydroxyphenylalanine, noradrenaline and adrenaline.

Cysteine

It is a sulpher containing amino acid. It is obtained frommethionine.

Dopa

Dopa is a neurotransmitter. It is converted to dopamine.Dopamine deficiency results in parkinsonism.

Tryptophan

Tryptophan is produced from Niacin. Niacin deficiencyresults in pellagra.

Proline

Proline is an amino acid that is hydroxylated tohydroxyproline in presence of vitamin c. If vitamin cdeficiency occurs. It leads to a disease condition calledScurvy. Scurvy is characterized by swollen gums andbleeding upon pressing the gums.

Glycine

Glycine is helpful in formation of bile acids. It combineswith colic acid to form glycocholate. It converts benzoicacid to hippuric acid in the liver. It is also a component ofglutathione. It is utilized in biosynthesis of creatine, hemeand purines.

Citrulline

It is a necessary component of urea cycle where it is

formed from ornithine and carbamoyl phosphate inpresence of an enzyme called ornithine transferase.Citrulline combines with aspartate and formarginosuccinate in urea cycle.

Ornithine

It is also a component of urea cycle. It is formed fromarginine by action of arginase. During this reaction ureasynthesis occurs and carbon dioxide is produced.

AMINO ACIDS IN PLANTS

Amino acids are present in plant and form protein. Plantssynthesize amino acids from the carbon and oxygen thais obtained from air and hydrogen from water in the soilAmino acids play important role to increase yield and

overall quality of crops. Amino acids are absorbedthrough stomas in plants. It has been observed thatamino acids influence the physiological activities of theplant. Plant mutants for amino acid transporter genes arenow being used to study the physiological functions ofmany of the cloned genes (Wolf et al., 1998).

Amino acid and GABA content in different cultivarsof Momordica charantia L.

A study was carried out to determine the variability oamino acid levels including gamma-aminobutyric acid(GABA) in six cultivars of bitter melon (Momordicacharantia L.) of different countries. Nikko and Peacockfrom Japan, Galaxy and Verde Buenas from Philippinesand two native cultivars from China and Korea wereselected for study. Cultivars varied considerably in theamounts of different amino acids Table 1. It wasconcluded that bitter melon cultivars varies in the amounof different amino acids and GABA and is a good sourceof amino acids and GABA in the development of foodsupplements (Yong et al., 2009).

Role of plasma amino acids in alcoholic and non-alcoholic fatty liver disease

It has been observed that alcohol interferes with theaction of gamma-amino butyric acid (GABA) and otheneurotransmitters. As alcohol metabolism occurs in livertherefore a pilot study was carried out to monitor thepatterns of changes in plasma amino-acidconcentrations. Plasma amino acids concentrationchanges were monitored in alcoholic and non alcoholicfatty liver. In this study, it was concluded that alcoholicliver disease presented a more deranged plasma aminoacid pattern than nonalcoholic (Mukherjee et al., 2010).

Phenylketonuria

Normally phenylalanine is converted to tyrosine. If thereis deficiency of phenylalanine hydroxylase, phenylalanineis not converted to tyrosine. As a result alternativecatabolites are produced. These catabolites are phenyacetate and phenyl lactate. Phenyl acetate is conjugatedwith glutamine and excreted as phenyl acetyl glutaminein urine producing mouse odour in urine. Accumulation ofphenyl alanine leads to defective serotonin formationimpaired melanin formation, children that are affected

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Table 1. Amino acids classification.

Essential amino acids Non essential amino acids Special amino acids

Lysine Cysteine GABA

Methionine Tyrosine DOPA

Valine Serine Citrulline

Tryptophan Alanine OrnithineIsoleucine Asparagines Taurine

Histidine Aspartic acid

Phenylalanine Glutamic acid

Threonine Glycine

Leucine Hydroxylysine

Arginine Proline

with this disease have fair hair and fair skin and arementally retarded, other features include seizure,psychosis and eczema.

Albinism

It is an inherited disorder that occurs due to deficiency ofenzyme tyrosinase. Tyrosinase is involved in synthesis ofmelanin. Due to deficiency of melanin, patient becomeswhite.

Alkaptonuria

It is a genetic disorder that occurs due to deficiency ofhomogentisic acid oxidase. In this disease, accumulation

of homogentisic acid occurs in the body. Manifestationsof this disease include dark urine and generalizedpigmentation of connective tissues.

DISCUSSION

Some amino acids are ketogenic amino acids that formketone bodies. Ketone bodies are chemical substancesthat the body forms when there is not enough insulin inthe blood. Ketone bodies are acetoacetate, beta hydroxylbutyrate and acetone. Ketone bodies are formed instarvation. Energy is produced from ketone bodies in

starvation. One acetoacetate give two acetyl Co A. Whenone acetyl Co. A enters TCA cycle, it produces 12 ATP.Glucogenic amino acids form glucose. Gluconeogenesisis a process in which glucose is formed from noncarbohydrate substances. Tryptophan is an essentialamino acid, containing indole ring in its structure. It isessential part of some proteins. Tryptophan producesserotonin. Increase serotonin level elevates the moodand decrease level causes depression. In the body 60mg of tryptophan produces 1 mg of Niacin. Niacindeficiency results in pellagra. Sign and symptoms ofPellagra include diarrhea, dementia and dermatitis. Some

amino acids help in formation of enzymes that catalyzethe chemical reaction (Usdin et al., 1967). Mutations inthe neutral amino acid transporter B0AT1 causesHartnup disorder. It is an autosomal recessive disorderIminoglycinuria is a multigene disorder. The proton aminoacid transporters PAT1 and PAT2, the IMINO transporteand the glycine transporter XT2 play important roles inthe resorption of glycine and proline. Recent research inthe cloning and identification of epithelial amino acidtransporters provides basis for the identification of genesthat are involved in Hartnup disorder and IminoglycinuriaSequence analysis of these genes is currently inprogress (Stefan, 2006). A study was carried out tomeasure amino acid contents in the brains of patientswith dominantly inherited cerebellar disorders. In thesepatients, clinical sign and symptoms were similar bubiochemically different disorders were observed. In one

disorder, moderate reduction of aspartate and glutamatecontents in cerebellar cortex was observed. In a seconddisorder, aspartate and glutamate were reducedmarkedly in cerebellar cortex and other brain areas. Inthird disorder, aspartate and glutamate contents werenormal in cerebellar cortex. In this study, it wasconcluded that reduction in amino acid content probablyimply loss of specific cerebellar neurons (Thomas et al.1981).

CONCLUSION

Amino acids are necessary for protein synthesis andhave various functions in the body. It is necessary to takethem in the diet because their deficiency results indecrease formation of protein or protein is not formed asa result protein deficiency may occur. It is concluded thatamino acid play important role in our body.

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