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The present findings show that the "editing" reaction is the latter half of a stepwise substrate selection and is not an ordinary error correction. Therefore, this reaction is unique among the essential editing or proofreading processes necessary to achieve high accuracy of information transfer in the central dogma (replication, transcription, and translation). The ATP consumption with regard to L-valine is nonproductive and is solely for substrate selection, which demonstrates the high cost of accuracy. On the other hand, it is interesting from an evolutionary viewpoint that all of the enzymes catalyzing the central steps of Ile-Val biosynthesis and metabolism do not distinguish, or can neglect the difference, between the two aliphatic amino acids, as was observed for the first catalytic site of IleRS. This finding implies that a putative ancestral enzyme of IleRS and ValRS might have actually had a similar dual specificity for L-isoleucine and L-valine in a primordial genetic code system.
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Synthetase.Biochemistry Vol.16 No.5 1977
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