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L-Methionine(CAS No. 63-68-3)

L-Methionine C5H11NO2S (cas 63-68-3) Molecular Structure

63-68-3 Structure

Identification and Related Records

【CAS Registry number】
2-Amino-4-methylthiobutanoic acid (S)-
Methionine, L-
2-Amino-4-(methylthio)butyric acid, (S)-
L-Homocysteine, S-methyl-
L-alpha-Amino-gamma-methylthiobutyric acid
(2S)-2-amino-4-(methylsulfanyl)butanoic acid
L-Methionine (AJI92
Methionine, L- (8CI)
Methionine (VAN)
L-2-Amino-4methylthiobutyric acid
(S)-2-amino-4-(methylthio)butyric acid
Methioninum [INN-Latin]
2-Amino-4-methylthiobutanoic acid
【Molecular Formula】
C5H11NO2S (Products with the same molecular formula)
【Molecular Weight】
【Canonical SMILES】
【MOL File】

Chemical and Physical Properties

White crystalline powder
1.206 g/cm3
【Melting Point】
276-279℃ (dec.)
【Boiling Point】
306.9 °C at 760 mmHg
【Flash Point】
139.4 °C
23.25 o (C=2, 6N HCL)
Soluble in water
Minute hexagonal plates from dilute alcohol
Colorless or white, lustrous plates or as white, crystalline powder
Stable. Incompatible with strong oxidizing agents.
【HS Code】
【Storage temp】
Store at RT.
【Spectral properties】
Specific optical rotation: 22.5 deg at 25 deg C/D (1 N HCl)
Specific optical rotation: -8.2 deg at 25 deg C/D (c = 0.8); +23.40 at 20 deg C/D (c = 5.0 in 3.0N HCl)
MASS: 54346 (NIST/EPA/MSDC Mass Spectral Database, 1990 version)
【Computed Properties】
Molecular Weight:149.21134 [g/mol]
Molecular Formula:C5H11NO2S
H-Bond Donor:2
H-Bond Acceptor:4
Rotatable Bond Count:4
Exact Mass:149.051049
MonoIsotopic Mass:149.051049
Topological Polar Surface Area:88.6
Heavy Atom Count:9
Formal Charge:0
Isotope Atom Count:0
Defined Atom Stereocenter Count:0
Undefined Atom Stereocenter Count:1
Defined Bond Stereocenter Count:0
Undefined Bond Stereocenter Count:0
Covalently-Bonded Unit Count:1
Feature 3D Acceptor Count:2
Feature 3D Donor Count:1
Feature 3D Anion Count:1
Feature 3D Cation Count:1
Feature 3D Hydrophobe Count:1
Effective Rotor Count:4
Conformer Sampling RMSD:0.6
CID Conformer Count:53

Safety and Handling

【Risk Statements】
【Safety Statements 】

Risk Statements:?33
R33:Danger of cumulative effects.?
Safety Statements: 24/25
S24/25: Avoid contact with skin and eyes.
WGK Germany: 2
RTECS: PD0457000
F: 10-23
HS Code: 29304010
Mildly toxic by ingestion and intraperitoneal routes. Human mutation data reported. An experimental teratogen. Experimental reproductive effects. An essential sulfur-containing amino acid. When heated to decomposition it emits very toxic fumes of NOx and SOx.

NF, feed 98%
USP and FCC grades; 99% feed grade
Racemate mixture of D- and L- methionine
【Exposure Standards and Regulations】
L-Methionine is a food additive permitted for direct addition to food for human consumption, as long as 1) the quantity of the substance added to food does not exceed the amount reasonably required to accomplish its intended physical, nutritive, or other technical effect in food, and 2) any substance intended for use in or on food is of appropriate food grade and is prepared and handled as a food ingredient.
Drug products containing certain active ingredients offered over-the-counter (OTC) for certain uses. A number of active ingredients have been present in OTC drug products for various uses, as described below. However, based on evidence currently available, there are inadequate data to establish general recognition of the safety and effectiveness of these ingredients for the specified uses: methionine is included in weight control drug products.
Methionine used as a nutrient and/or dietary supplement in animal drugs, feeds, and related products is generally recognized as safe when used in accordance with good manufacturing or feeding practice.

General Information: As in any fire, wear a self-contained breathing apparatus in pressure-demand, MSHA/NIOSH (approved or equivalent), and full protective gear. Dusts at sufficient concentrations can form explosive mixtures with air.
Extinguishing Media: For small fires, use water spray, dry chemical, carbon dioxide or chemical foam.?
Handling: Minimize dust generation and accumulation. Avoid breathing dust, vapor, mist, or gas. Avoid contact with skin and eyes.
Storage: Store in a cool, dry place. Store in a tightly closed container. Keep refrigerated. (Store below 4°C/39°F.)

【Octanol/Water Partition Coefficient】
log Kow = -1.87

Reported in EPA TSCA Inventory. EPA Genetic Toxicology Program.

【Disposal Methods】
SRP: Expired or waste pharmaceuticals shall carefully take into consideration applicable DEA, EPA, and FDA regulations. It is not appropriate to dispose by flushing the pharmaceutical down the toilet or discarding to trash. If possible return the pharmaceutical to the manufacturer for proper disposal being careful to properly label and securely package the material. Alternatively, the waste pharmaceutical shall be labeled, securely packaged and transported by a state licensed medical waste contractor to dispose by burial in a licensed hazardous or toxic waste landfill or incinerator.
SRP: At the time of review, regulatory criteria for small quantity disposal are subject to significant revision, however, household quantities of waste pharmaceuticals may be managed as follows: Mix with wet cat litter or coffee grounds, double bag in plastic, discard in trash.
SRP: Criteria for land treatment or burial (sanitary landfill) disposal practices are subject to significant revision. Prior to implementing land disposal of waste residue (including waste sludge), consult with environmental regulatory agencies for guidance on acceptable disposal practices.

Use and Manufacturing

【Use and Manufacturing】
Methods of Manufacturing

The production method of choice for L-methionine is still the enzymatic resolution of racemic N-acetyl-methionine using acylase from Aspergillus oryzae. The production is carried out in a continuously operated fixed-bed or enzyme membrane reactor. Alternatively, L-methionine may be produced by microbial conversion of the corresponding 5-substituted hydantoin. With growing cells of Pseudomonas sp. strain NS671, D,L-5-(2-methylthioethyl)hydantoin was converted to L-methionine; a final concentration of 34 g/L and a molar yield of 93% have been obtained.
The most economic way for production of D,L-methionine is the chemical process based on acrolein, methyl mercaptan, hydrogen cyanide, and ammonium carbonate. beta-Methylthiopropionaldehyde, formed by addition of methyl mercaptan to acrolein, is the intermediate that reacts with hydrogen cyanide to give alpha-hydroxy-gamma-methylthiobutyronitrile. Treatment with ammonium carbonate leads to 5-(beta-methylthioethyl)hydantoin that is saponified by potassium carbonate giving D,L-methionine in up to 95% yield, calculated on acrolein. /D,L-Methionine/
U.S. Production

(1992) No data
World market for L-methionine in 1982: 150 tons; World market for DL-methionine in 1982: 110,000 tons
Production volumes for non-confidential chemicals reported under the Inventory Update Rule. Year Production Range (pounds) 1986 10 thousand - 500 thousand 1990 No Reports 1994 No Reports 1998 No Reports 2002 No Reports
Consumption Patterns

Used almost exclusively to improve the nutritive value of animal feeds /DL-Methionine/

Feed additive, vegetable oil enrichment, single-cell protein dl mixt.

Biomedical Effects and Toxicity

【Therapeutic Uses】
A sulfur containing essential amino acid that is important in many body functions. It is a chelating agent for heavy metals
Methionine ... enhances the synthesis of glutathione and is used as an alternative to acetylcysteine in the treatment of paracetamol poisoning.
... Many of signs of toxicity /of selenium poisoning/ can be prevented by high-protein diets, and by methionine in the presence of Vitamin E.
In Europe, oral methionine (10 g over 12 hours) is approved as an agent to restore depleted glutathione stores and prevent hepatotoxicity after large acetaminophen ingestions. N-Acetyl-L-cysteine remains the preferred antidote for acetaminophen overdose in the United States, Canada, Scotland, and most of England.
Lipotropic agent
Medication: Hepatoprotectant; antidote (acetaminophen poisoning); urinary acidifier.
Medication (Vet): Nutritional supplement; urinary acidifier.
One hundred thirty-two cases of severe acetaminophen (paracetamol) poisoning were treated with oral methionine. Seven of 96 patients who received the antidote within ten hours of ingestion of the overdose had severe liver damage (aspartate transaminase level, greater than 1,000 IU/L), but none of these patients died. Thirty-six patients received methionine between ten and 24 hours of ingestion; severe liver damage occurred in 47%, and two patients died. The treatment protocol for oral methionine is simple, and therapy is complete within 12 hours as compared with three days for oral acetylcysteine and 20 hours for intravenous acetylcysteine. Side effects from methionine were unimportant. Oral methionine is as effective as acetylcysteine in preventing severe liver damage and death after acetaminophen overdose. However, as with acetylcysteine, it must be given within ten hours of ingestion to be effective. [Vale JA et al; Arch Intern Med 141 (3 Spec No): 394-6 (1981). Available from, as of March 17, 2010:]
【Biomedical Effects and Toxicity】
... Rats were fed diets containing [(14)C-methyl]l-methionine ... with 6% of sodium formate, and conversion of (14)C into [(14)C]formate was measured in urine and exhaled air (as (14)CO2) ... Total oxidation of [(14)C-methyl] into CO2, amounted to 60-87% for methionine ...
Although the free amino acids dissolved in the body fluids are only a very small proportion of the body's total mass of amino acids, they are very important for the nutritional and metabolic control of the body's proteins. ... Although the plasma compartment is most easily sampled, the concentration of most amino acids is higher in tissue intracellular pools. Typically, large neutral amino acids, such as leucine and phenylalanine, are essentially in equilibrium with the plasma. Others, notably glutamine, glutamic acid, and glycine, are 10- to 50-fold more concentrated in the intracellular pool. Dietary variations or pathological conditions can result in substantial changes in the concentrations of the individual free amino acids in both the plasma and tissue pools. /Amino acids/
After ingestion, proteins are denatured by the acid in the stomach, where they are also cleaved into smaller peptides by the enzyme pepsin, which is activated by the increase in stomach acidity that occurs on feeding. The proteins and peptides then pass into the small intestine, where the peptide bonds are hydrolyzed by a variety of enzymes. These bond-specific enzymes originate in the pancreas and include trypsin, chymotrypsins, elastase, and carboxypeptidases. The resultant mixture of free amino acids and small peptides is then transported into the mucosal cells by a number of carrier systems for specific amino acids and for di- and tri-peptides, each specific for a limited range of peptide substrates. After intracellular hydrolysis of the absorbed peptides, the free amino acids are then secreted into the portal blood by other specific carrier systems in the mucosal cell or are further metabolized within the cell itself. Absorbed amino acids pass into the liver, where a portion of the amino acids are taken up and used; the remainder pass through into the systemic circulation and are utilized by the peripheral tissues. /Amino acids/
Protein secretion into the intestine continues even under conditions of protein-free feeding, and fecal nitrogen losses (ie, nitrogen lost as bacteria in the feces) may account for 25% of the obligatory loss of nitrogen. Under this dietary circumstance, the amino acids secreted into the intestine as components of proteolytic enzymes and from sloughed mucosal cells are the only sources of amino acids for the maintenance of the intestinal bacterial biomass. ... Other routes of loss of intact amino acids are via the urine and through skin and hair loss. These losses are small by comparison with those described above, but nonetheless may have a significant impact on estimates of requirements, especially in disease states. /Amino acids/
About 11 to 15 g of nitrogen are excreted each day in the urine of a healthy adult consuming 70 to 100 g of protein, mostly in the form of urea, with smaller contributions from ammonia, uric acid, creatinine, and some free amino acids. These are the end products of protein metabolism, with urea and ammonia arising from the partial oxidation of amino acids. Uric acid and creatinine are indirectly derived from amino acids as well. The removal of nitrogen from the individual amino acids and its conversion to a form that can be excreted by the kidney can be considered as a two-part process. The first step usually takes place by one of two types of enzymatic reactions: transamination or deamination. Transamination is a reversible reaction that uses ketoacid intermediates of glucose metabolism (e.g., pyruvate, oxaloacetate, and alpha-ketoglutarate) as recipients of the amino nitrogen. Most amino acids can take part in these reactions, with the result that their amino nitrogen is transferred to just three amino acids: alanine from pyruvate, aspartate from oxaloacetate, and glutamate from alpha-ketoglutarate. Unlike many amino acids, branched-chain amino acid transamination occurs throughout the body, particularly in skeletal muscle. Here the main recipients of amino nitrogen are alanine and glutamine (from pyruvate and glutamate, respectively), which then pass into the circulation. These serve as important carriers of nitrogen from the periphery (skeletal muscle) to the intestine and liver. In the small intestine, glutamine is extracted and metabolized to ammonia, alanine, and citrulline, which are then conveyed to the liver via the portal circulation. Nitrogen is also removed from amino acids by deamination reactions, which result in the formation of ammonia. A number of amino acids can be deaminated, either directly (histidine), by dehydration (serine, threonine), by way of the purine nucleotide cycle (aspartate), or by oxidative deamination (glutamate). ... Glutamate is also formed in the specific degradation pathways of arginine and lysine. Thus, nitrogen from any amino acid can be funneled into the two precursors of urea synthesis, ammonia and aspartate. /Amino acids/
It was noted that blood concentrations could be considerably higher when amino acids were consumed as supplements as opposed to a component of protein in food. /Amino acids/
Comparison of the Pool Sizes of Free and Protein-Bound Amino Acids in Rat Muscle Indispensable amino acids Protein (umol/g Wet Weight) Free (umol/g Wet Weight) Protein Free Ratio (umol/g Wet Weight) Histidine 26 0.39 67 Isoleucine 50 0.16 306 Leucine 109 0.20 556 Lysine 58 1.86 31 Methionine 36 0.16 225 Phenylalanine 45 0.07 646 Threonine 60 1.94 31 Valine 83 0.31 272
Although it seems clear that the efficiency of dietary protein digestion (in the sense of removal of amino acids from the small intestinal lumen) is high, there is now good evidence to show that nutritionally significant quantities of indispensable amino acids are metabolized by the tissues of the splanchnic bed, including the mucosal cells of the intestine. Thus, less than 100% of the amino acids removed from the intestinal lumen appear in the peripheral circulation, and the quantities that are metabolized by the splanchnic bed vary among the amino acids, with intestinal threonine metabolism being particularly high. /Amino acids/
Using a double-lumen tube perfusion system the rates of absorption of L-methionine and glucose from a 30 cm segment of the jejunum were estimated in eight relatively normal Zambian African subjects. The effect of each substrate on the absorption of the other has also been investigated. The solutions perfused were given at 12.0 ml/L/min, and contained 100 m-mole/L of L-methionine, 100 m-mole/L of L-methionine and 150 m-mole/L of glucose or 150 m-mole/L of glucose. The presence of glucose in the perfusing fluid did not significantly alter the mean absorption rate of methionine ... . Five subjects had a transitory psychiatric disturbance after the investigation. The cause of this is not clear, but was probably caused by the absorption of a break-down product of methionine from the large intestine. [Cook GC; J Physiol 221 (3): 707-14 (1972). Available from, as of March 17, 2010:] PubMed Abstract
Six middle-aged male volunteers were infused with L-[methyl-2H3,1-13C]methionine before (for 3 hr) and after (for 3 additional hours) an euglycemic hyperinsulinemic (150 mU/l) clamp. Steady-state methionine and homocysteine kinetics were determined using either plasma (ie, those of methionine) or intracellular (ie, those of plasma homocysteine) enrichments. By use of plasma enrichments, insulin decreased methionine rate of appearance (Ra; both methyl- and carbon Ra) by 25% (P
... Female rats /were/ offered diets with either adequate or excess methionine (additional methyl groups) with or without folate and choline (impaired methyl group transfer) for 5 wk. Whole body and tissue metabolism was measured based on isotopomer analysis following infusion with either [1-(13)C,methyl-(2)H3]methionine or [U-(13)C]methionine plus [1-(13)C]homocysteine. Although the fraction of intracellular methionine derived from methylation of homocysteine was highest in liver (0.18-0.21), most was retained. In contrast, the pancreas exported to plasma more of methionine synthesized de novo. The pancreas also exported homocysteine to plasma, and this matched the contribution from liver. Synthesis of methionine from homocysteine was reduced in most tissues with excess methionine supply and was also lowered in liver (P

Environmental Fate and Exposure Potential

【Environmental Fate/Exposure Summary】
TERRESTRIAL FATE: Based on a classification scheme(1), an estimated Koc value of 8(SRC), determined from a log Kow of -1.87(2) and a regression-derived equation(3), indicates that (L)-methionine is expected to have very high mobility in soil(SRC). The pKa values of (L)-methionine are 2.28 and 9.21(4), indicate that this compound will exist as a zwitterion which may affect its adsorption to soils and sediments(SRC). Volatilization from moist soil is not expected because ions do not volatilize(SRC). (L)-Methionine is not expected to volatilize from dry soil surfaces(SRC) based upon an estimated vapor pressure of 8.1X10-8 mm Hg at 25 deg C(SRC), determined from a fragment constant method(5). Using a laboratory activated sludge system, (L)-methionine exhibited an 80% theoretical BOD reduction in 16 days, producing 3-mercaptopropionate, methanethiol and dimethylsulfide(6); this suggests that biodegradation may be an important environmental fate process in soil(SRC).
AQUATIC FATE: Based on a classification scheme(1), an estimated Koc value of 8(SRC), determined from a log Kow of -1.87(2) and a regression-derived equation(3), indicates that (L)-methionine is not expected to adsorb to suspended solids and sediment(SRC). The pKa values of 2.28 and 9.21(4) indicates (L)-methionine will exist as a zwitterion at pH values of 5 to 9 and therefore volatilization from water surfaces is not expected to be an important fate process(5). According to a classification scheme(6), an estimated BCF of 3(SRC), from its log Kow(2) and a regression-derived equation(7), suggests the potential for bioconcentration in aquatic organisms is low(SRC). Using a laboratory activated sludge system, (L)-methionine exhibited an 80% theoretical BOD reduction in 16 days, producing 3-mercaptopropionate, methanethiol and dimethylsulfide(8); this suggests that biodegradation may be an important environmental fate process in water(SRC).
AQUATIC FATE: (L)-Methionine has been shown to degrade in sunlit natural water through a photo-sensitized oxidation involving singlet oxygen(1,2); assuming that the top meter of sunlit natural water has a singlet oxygen concn of 4X10-14 M, the photooxidation half-life for the reaction (L)-methionine with singlet oxygen has been estimated to be about 200 hr at pH 6-11(1); the near-surface photooxidation rate (via singlet oxygen) of (L)-methionine in Okefenokee Swamp water from Georgia is predicted to be about 3 hr(2). Bioconcentration and volatilization are not expected to important fate processes because of its high water solubility(SRC).
ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), (L)-methionine, which has an estimated vapor pressure of 8.1X10-8 mm Hg at 25 deg C(SRC), determined from a fragment constant method(2), will exist in both the vapor and particulate phases in the ambient atmosphere. Vapor-phase (L)-methionine is degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals(SRC); the half-life for this reaction in air is estimated to be 7.5 hours(SRC), calculated from its rate constant of 5.1X10-11 cu cm/molecule-sec at 25 deg C(SRC) that was derived using a structure estimation method(3). (L)-Methionine does not contain chromophores that absorb at wavelengths >290 nm(4) and therefore is not expected to be susceptible to direct photolysis by sunlight(SRC).

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