DL-Methionin

DL-Methionine Chemische Eigenschaften,Einsatz,Produktion Methoden

• ERSCHEINUNGSBILD

  FARBLOSE KRISTALLE ODER WEISSES PULVER.

• CHEMISCHE GEFAHREN

  Zersetzung beim Erhitzen unter Bildung giftiger Rauche mit Schwefeloxiden und Stickstoffoxiden.

• ARBEITSPLATZGRENZWERTE

  TLV nicht festgelegt (ACGIH 2005).
  MAK nicht festgelegt (DFG 2005).
  

• AUFNAHMEWEGE

  Aufnahme in den Körper durch Verschlucken.

• LECKAGE

  Verschüttetes Material in Behältern sammeln. Reste sorgfältig sammeln. An sicheren Ort bringen.

• R-Sätze Betriebsanweisung:

  R33:Gefahr kumulativer Wirkungen.
  R36/37/38:Reizt die Augen, die Atmungsorgane und die Haut.

• S-Sätze Betriebsanweisung:

  S24/25:Berührung mit den Augen und der Haut vermeiden.
  S36:DE: Bei der Arbeit geeignete Schutzkleidung tragen.
  S26:Bei Berührung mit den Augen sofort gründlich mit Wasser abspülen und Arzt konsultieren.

• Beschreibung

  Methionine is an α-amino acid with the chemical formula HO₂CCH(NH₂)CH₂CH₂SCH₃. This essential amino acid is classified as nonpolar. This amino-acid is coded by the initiation codon AUG which indicates mRNA's coding region where translation into protein begins.

• Chemische Eigenschaften

  White crystalline powder

• Chemische Eigenschaften

  d,l-Methionine has a characteristic odor. It is an essential amino acid and is also used as a nutrient and dietary supplement.

• Chemische Eigenschaften

  White, crystalline platelets or powder having a characteristic odor. One g dissolves in about 30 mL of water. It is soluble in dilute acids and in solutions of alkali hydroxides. It is very slightly soluble in alcohol, and practically insoluble in ether. It is optically inactive. The pH of a 1 in 100 solution is between 5.6 and 6.1. This substance may be prepared by addition of methanethiol to acrolein; by chemical conversion of methylthiopropionic aldehyde.

• Occurrence

  High levels of methionine can be found in eggs, sesame seeds, Brazil nuts, fish, meats and some other plant seeds; methionine is also found in cereal grains. Most fruits and vegetables contain very little of it. Most legumes are also low in methionine. Racemic methionine is sometimes added as an ingredient to pet foods.

• Verwenden

  An essential nonpolar amino acid with oxidative stress defense properties

• Verwenden

  Production of volatile compounds related to the flavour of foods from the Strecker degradation of DL-methionine. Addition of methionine in appropriate amounts to these foods might be expected to improve protein value. Economically, DL-methionine would be preferable.

• Verwenden

  DL-Methionine is sometimes given as a supplement to dogs; it helps keep dogs from damaging grass by reducing the pH of the urine.
  Methionine is allowed as a supplement to organic poultry feed under the US certified organic program.

• Definition

  ChEBI: A sulfur-containing amino acid that is butyric acid bearing an amino substituent at position 2 and a methylthio substituent at position 4.

• synthetische

  By addition of methanethiol to acrolein; by chemical conversion of methylthiopropionic aldehyde.

• Trademarks

  Pedameth (Forest).

• Biosynthese

  As an essential amino acid, methionine is not synthesized de novo in humans, who must ingest methionine or methioninecontaining proteins. In plants and microorganisms, methionine is synthesized via a pathway that uses both aspartic acid and cysteine. First, aspartic acid is converted via β-aspartyl-semialdehyde into homoserine, introducing the pair of contiguous methylene groups. Homoserine converts to O-succinyl homoserine, which then reacts with cysteine to produce cystathionine, which is cleaved to yield homocysteine. Subsequent methylation of the thiol group by folates affords methionine. Both cystathionine-γ-synthase and cystathionine- β-lyase require pyridoxyl-5′-phosphate as a cofactor, whereas homocysteine methyltransferase requires vitamin B12 as a cofactor.

• Biotechnologische Produktion

  DL-Methionine is the second amino acid that is almost exclusively manufactured by chemical synthesis. The process used today was originally developed by Werner Schwarze at Degussa in the 1940s, and has been continually improved and refined since. Today DL-methionine is manufactured in several plants, each with a capacity of more than 100,000 tonnes. To operate the process on an industrial scale also requires back-integration into the key hazardous raw materials acrolein, methyl mercaptan, and hydrogen cyanide. After the formation of the hydantoin, the key step is alkaline hydrolysis of the hydantoin, to produce methionine directly in up to 95 % yield based on acrolein.

• Biologische Funktion

  Together with cysteine, methionine is one of two sulfurcontaining proteinogenic amino acids. Its derivative S-adenosyl methionine (SAM) serves as a methyl donor. Methionine is an intermediate in the biosynthesis of cysteine, carnitine, taurine, lecithin, phosphatidylcholine, and other phospholipids. Improper conversion of methionine can lead to atherosclerosis.
  This amino acid is also used by plants for synthesis of ethylene. The process is known as the Yang Cycle or the methionine cycle.
  Methionine is one of only two amino acids encoded by a single codon (AUG) in the standard genetic code (tryptophan, encoded by UGG, is the other). The codon AUG is also the most common eukaryote "Start" message for a ribosome that signals the initiation of protein translation from mRNA when the AUG codon is in a Kozak consensus sequence. As a consequence, methionine is often incorporated into the N-terminal position of proteins in eukaryotes and archaea during translation, although it can be removed by post-translational modification. In bacteria, the derivative Nformylmethionine is used as the initial amino acid.

• Allgemeine Beschreibung

  DL-Methionine is an essential amino acid containing sulphur. Methionine consists of an asymmetric carbon and exists as D (dextrogyre) and L (levogyre) optical isomers. The L-methionine is considered as biologically active. The racemic mixture of D and L-isomers forms DL-methionine, which is the commercially available methionine.

• Biochem/physiol Actions

  Methionine offers protection against disorders related to hair, skin and nails. It elevates lecithin production in the liver and thereby reduces cholesterol level. It naturally serves as a heavy metal chelating agent, regulating ammonia concentration in the urine. This ameliorates bladder irritation. Methionine is also known to induce hair growth.

• Sicherheitsprofil

  Moderately toxic by ingestion and other routes. An experimental teratogen. Experimental reproductive effects. When heated to decomposition it emits toxic fumes of SOx and NOx. See also 1-METHIONINE.

• läuterung methode

  Crystallise it from hot water or EtOH. Also purify it by dissolving it in H2O and passing through an Amberlite IR-120 resin (NH4+ form). The eluate is concentrated and then passed through Amberlite IR-4B resin, and this eluate is evaporated to dryness. The residue is washed with EtOH, then Me2CO, dried and recrystallised from aqueous EtOH (colourless plates) [Baddiley & Jamieson J Chem Soc 4283 1954]. [Greenstein & Winitz The Chemistry of the Amino Acids J. Wiley, Vol 3 p 2125 1961, Beilstein 4 IV 3190.]

• Other biochemical pathways

  Although mammals cannot synthesize methionine, they can still use it in a variety of biochemical pathways:
  Generation of homocysteine Methionine is converted to S-adenosyl methionine (SAM) by (1) methionine adenosyltransferase.
  SAM serves as a methyl-donor in many (2) methyl transferase reactions, and is converted to S-adenosylhomocysteine (SAH).
  (3) Adenosyl homocysteinase converts SAH to homocysteine.
  There are two fates of homocysteine: it can be used to regenerate methionine, or to form cysteine.
  Regeneration of methionine
  Methionine can be regenerated from homocysteine via methionine synthase in a reaction that requires Vitamin B12 as a cofactor.
  Homocysteine can also be remethylated using glycine betaine (NNN-trimethyl glycine, TMG) to methionine via the enzyme betainehomocysteine methyltransferase (E.C.2.1.1.5, BHMT). BHMT makes up to 1.5% of all the soluble protein of the liver, and recent evidence suggests that it may have a greater influence on methionine and homocysteine homeostasis than methionine synthase.

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