Fidelity of aminoacylation by rat‐liver tyrosyl‐tRNA synthetase

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Abstract
The possibility of change in the rate of misrecognition of amino acids by rat liver tyrosyl-tRNA synthetase during aging was investigated. Frequency of misrecognition of phenylalanine vs tyrosine was determined at two temperatures by competitive assay using partially purified enzymes. At 25.degree.C, the error frequencies were 5.17 .times. 10-8 and 8.24 .times. 10-8 in young and old animals, respectively. These values are much below the reported error frequencies for the prokaryotic enzymes: i.e. .apprxeq. 5 .times. 10-6. Although the fidelity of tyrosyl-tRNA synthetase from old animals appeared to be slightly lower, the difference was not statistically significant. AT 37.degree.C, the error frequencies were increased 1.3-1.5-fold, but again the difference between young and old animals was not significant. To our knowledge, this is the first report in which fidelity of aminoacyl-tRNA synthetase of animals of various ages has been compared using natural amino acids.