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(mĕthī`ənēn), organic compound, one of the 20 amino acidsamino acid
, any one of a class of simple organic compounds containing carbon, hydrogen, oxygen, nitrogen, and in certain cases sulfur. These compounds are the building blocks of proteins.
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 commonly found in animal proteins. Only the L-stereoisomer appears in mammalian protein. It is one of the several essential amino acids needed in the diet; the human body cannot synthesize it from simpler metabolites. It is an important source of dietary sulfur. Methionine reacts with adenosine triphosphateadenosine triphosphate
(ATP) , organic compound composed of adenine, the sugar ribose, and three phosphate groups. ATP serves as the major energy source within the cell to drive a number of biological processes such as photosynthesis, muscle contraction, and the synthesis of
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 to form S-adenosyl methionine, a potent donor of methyl groups (composed of one carbon and three hydrogen atoms); S-adenosyl methionine is the principal methyl donor in the body and contributes to the synthesis of many important substances, including epinephrineepinephrine
, hormone important to the body's metabolism, also known as adrenaline. Epinephrine, a catecholamine, together with norepinephrine, is secreted principally by the medulla of the adrenal gland.
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 and choline (see acetylcholineacetylcholine
, a small organic molecule liberated at nerve endings as a neurotransmitter. It is particularly important in the stimulation of muscle tissue. The transmission of an impulse to the end of the nerve causes it to release neurotransmitter molecules onto the surface of
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; vitaminvitamin,
group of organic substances that are required in the diet of humans and animals for normal growth, maintenance of life, and normal reproduction. Vitamins act as catalysts; very often either the vitamins themselves are coenzymes, or they form integral parts of coenzymes.
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). Since methionine is the only essential amino acid not present in significant amounts of soybeans, it is produced commercially as an additive for soybean meal. Methionine was isolated from casein (milk protein) in 1922, and its structure was proved by laboratory synthesis in 1928.
The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



α-amino-γ-methylmercaptobutyric acid, CH3SCH2CH2CH(NH2)COOH; a sulfur-bearing monocarboxylic amino acid. Methionine exists in D- and L- forms and in a racemic DL- form. L-methionine is a component of most vegetable and animal proteins. It was isolated in 1922 from the products of the acid hydrolysis of casein.

In mammals and man, methionine is a donor of methylene groups in the body. In its S-adenosyl form (active methionine, a product of the reaction of methionine with ATP in the presence of Mg2+ ions), methionine participates in enzymic transmethylation processes, which lead to the formation of choline, adrenalin, and other biologically important substances. It also serves as a source of sulfur in the biosynthesis of cysteine.

The initial substance in the biosynthesis of methionine is aspartic acid, which undergoes a series of conversions to methionine’s immediate precursor, homocysteine. This series of conversions can occur only in certain microorganisms and plants. Homocysteine can also undergo methylation in mammals, enzymically or by direct transfer of a methyl group from donor molecules.

Methionine is an essential amino acid, the daily adult human requirement for which is 2.5–3 g. Methionine deficiency in the diet of animals and man leads to impairment of protein biosyn-thesis, retardation of growth and development, and severe functional disorders. Synthetic methionine, produced industrially from propylene, is used medicinally and to enrich fodders and food. The D- and L- forms of methionine are of equal value, since they are capable of interconversion in the body.


Maister, A. Biokhimiia aminokislot. Moscow, 1961. (Translated from English.)


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


C5H11O2NS An essential amino acid; furnishes both labile methyl groups and sulfur necessary for normal metabolism.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
They found that a low dose of chemotherapy, which on its own had no effect on colorectal cancer, led to "marked inhibition of tumour growth" when combined with methionine restriction.
This paves the way for the development of next-generation drugs that target this dependence on methionine," said Dr Wang Zhenxun, the first author of this study.
The particle size distribution and polydispersity (zeta potential) of the nanoemulsified methionine and cysteine were analyzed by dynamic light scattering correlation spectroscopy using a high-performance particle sizer instrument (Malvern Instruments, Malvern, UK).
The results of analysis indicated that concentrations of amino acids were significantly different between patients and healthy individuals (p<0.05), except methionine that there was not significant difference, as shown in Figure 1.
Feed (FI) and methionine + cysteine intake (MCI), body weight gain (BWG), feed conversion (FC), and uniformity (UNIF) were assessed in all experiment periods.
Human myeloperoxidase (MPO), hydrogen peroxide ([H.sub.2][O.sub.2]), potassium chloride (KCl), methionine, methionine sulfoxide, indigo carmine, isatin sulfonic acid, vinylbenzoic acid, 4-carboxybenzaldehyde, potassium orthophosphate buffer (K[H.sub.2]P[O.sub.4]), and acetonitrile were purchased from Sigma Aldrich.
Methionine and cystine are the first-limiting amino acids for fur animals, which have a significant effect on fur growth and quality (Dahlman et al., 2004).
Cystadane is a prescription pharmaceutical product that helps to remove homocysteine from the blood by converting excess homocysteine to methionine.
Elevated Hcy levels were successfully induced by using 1% w/v of methionine in water for 8wks in the db/db mice of the DM (methionine) and DM (methionine + SAA) groups and were evidenced by a 6-fold of increment when compared to the other groups without taking methionine in water (Figure 3).
Synthesis of L- and D-[methyl-[sup]11C] methionine. J Nucl Med 1987;28:1037-40.
The metabolism of homocysteine occurs via two major pathways, the first and most predominant of these is the remethylation of Hcy to methionine. Vitamin [B.sub.6] is also involved in this process, as it functions as a cofactor for the enzyme Cystathionine [beta]-synthase (CBS), the first, and rate-limiting enzyme in the transsulfuration pathway, which is required to convert Hcy to cystathioine.