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Aminoacyl tRNA synthetase
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Aminoacyl tRNA synthetase : ウィキペディア英語版
Aminoacyl tRNA synthetase

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)
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