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An aminoacyl tRNA synthetase (aaRS) is an enzyme that attaches the appropriate amino acid onto its tRNA. It does so by catalyzing the esterification of a specific cognate amino acid or its precursor to one of all its compatible cognate tRNAs to form an aminoacyl-tRNA. This is sometimes called "charging" or "loading" the tRNA with the amino acid. Once the tRNA is charged, a ribosome can transfer the amino acid from the tRNA onto a growing peptide, according to the genetic code. Aminoacyl tRNA therefore plays an important role in DNA translation, the expression of genes to create proteins. ==Mechanism== The synthetase first binds ATP and the corresponding amino acid (or its precursor) to form an aminoacyl-adenylate, releasing inorganic pyrophosphate (PPi). The adenylate-aaRS complex then binds the appropriate tRNA molecule, and the amino acid is transferred from the aa-AMP to either the 2'- or the 3'-OH of the last tRNA nucleotide (A76) at the 3'-end. The mechanism can be summarized in the following reaction series: # amino acid + ATP → aminoacyl-AMP + PPi # aminoacyl-AMP + tRNA → aminoacyl-tRNA + AMP Summing the two reactions, the overall reaction is as following: amino acid + tRNA + ATP → aminoacyl-tRNA + AMP + PPi The sum of these three reactions is highly exergonic, These 3 reactions can be combined to produce: amino acid + tRNA + ATP + H20 → aminoacyl-tRNA + AMP + 2PPi Some synthetases also mediate a proofreading reaction to ensure high fidelity of tRNA charging; if the tRNA is found to be improperly charged, the aminoacyl-tRNA bond is hydrolyzed. 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「Aminoacyl tRNA synthetase」の詳細全文を読む スポンサード リンク
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