Enzymatic Deacylation of Methionyl‐tRNAfMef Catalysed by Methionyl, Isoleucyl and Phenylalanyl‐tRNA Synthetases

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Abstract
Native and trypsin‐modified methionyl, isoleucyl and phenylalanyl‐tRNA synthetases from Escherichia coli catalyze the deacylation of methionyl‐tRNAtMet. This activity, which is pH dependent, requires the presence of MgCl2 or spermidine which are known to structure the aminoacyl‐tRNA. Investigation of the effects of cognate amino acids on the rate of enzymatic deacylation of methionyl‐tRNAtMet, reveals strikingly different behaviours of native and trypsin‐modified methionyl‐tRNA synthetases.Kinetic parameters for the deacylation of methionyl‐tRNAtmet catalyzed by native methionyl and isoleucyl‐tRNA synthetases are compared in the presence of MgCl2 and provide identical Km values of 0.2 μM while their V values, are 0.05 and 0.02 s−1, respectively. This indicates similar enzymatic efficiencies per active site and emphasizes the lack of specificity of the reaction.