Methionine

Methionine is an essential, nonpolar proteinogenic amino acid containing a sulfur atom. It can be converted to cysteine.

Metabolism
As an essential amino acid, methionine cannot be synthesized and must be obtained from the diet.

Convert to SAM
S-adenosylmethionine, or active methionine, is a nucleoside capable of methylating other substances and is therefore essential in many metabolic pathways (choline, creatine, adrenaline, ...). This property is due to the presence of a positively charged sulfur atom. The synthesis of SAM from methionine requires ATP and is catalyzed by the appropriate transferase.

Conversion to Cysteine ​​
The starting substance of conversion to cysteine ​​is S-adenosylmethionine. This is converted into S-adenosylhomocysteine ​​by splitting off the methyl, which then changes into homocysteine. After its fusion with serine, cystathion is formed. It disintegrates immediately, but the sulfur atom remains on the serine skeleton. Homocysteine ​​is left to homoserine, which is converted to succinyl-CoA via propionyl-CoA.

Task in translation
As methionine is encoded by the initiation codon AUG, it forms the cap at the N-terminus of each newly synthesized peptide. However, this is usually removed as part of post-translational modifications.

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 * Amino Acids