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|Section2= |Section3= }} ''N''-Formylmethionine (fMet) is a derivative of the amino acid methionine in which a formyl group has been added to the amino group. It is specifically used for initiation of protein synthesis from bacterial and organellar genes, and may be removed post-translationally. fMet plays a crucial part in the protein synthesis of bacteria, mitochondria and chloroplasts. It is not used in cytosolic protein synthesis of eukaryotes, where eukaryotic nuclear genes are translated. It is also not used by Archaea. In the human body, fMet is recognized by the immune system as foreign material, or as an alarm signal released by damaged cells, and stimulates the body to fight against potential infection. ==Function in protein synthesis== fMet is a starting residue in the synthesis of proteins in bacteria, and, consequently, is located at the N-terminus of the growing polypeptide. fMet is delivered to the ribosome (30S) - mRNA complex by a specialized tRNA (tRNAfMet) which has a 3'-UAC-5' anticodon that is capable of binding with the 5'-AUG-3' start codon located on the mRNA. fMet is coded by the same codon as methionine, AUG. However, AUG is also the translation initiation codon. When the codon is used for initiation, fMet is used instead of methionine, thereby forming the first amino acid of the nascent peptide chain. When the same codon appears later in the mRNA, normal methionine is used. Many organisms use variations of this basic mechanism. The addition of the formyl group to methionine is catalyzed by the enzyme methionyl-tRNA formyltransferase. This modification is done after methionine has been loaded onto tRNAfMet by aminoacyl-tRNA synthetase. Note that methionine can be loaded either onto tRNAfMet or tRNAMet. However, transformylase will catalyze the addition of the formyl group to methionine only if methionine has been loaded onto tRNAfMet and not onto tRNAMet. This methionine is removed from majority of proteins (both host and recombinant) by methionine aminopeptidase (MAP). Before aminopeptidase can remove the N-terminal methionine, it must be deformylated by peptide deformylase. The mitochondria of eukaryote cells, including those of humans, and the chloroplasts of plant cells also initiate protein synthesis with N-formylmethionine (see N-Formylmethionine-leucyl-phenylalanine). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「N-Formylmethionine」の詳細全文を読む スポンサード リンク
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