Methionyl‐tRNA Synthetase from Escherichia coli

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Abstract
Both the aminoacylation and isotopic ATP‐PPi exchange activities of native and trypsin‐modified methionyl–tRNA synthetases from Escherichia coli are specifically inactivated by incubation in the presence of periodate‐treated initiator tRNAMet.The inactivation proceeds through the formation of a reversible Schiff's base between the ɛ‐amino group of a lysine within the catalytic center of the enzyme and the 2′,3′‐aldehyde groups created at the 3′‐terminal ribose of tRNA. The Schiff's base may be stabilized by reduction with sodium borohydride.Intact tRNAfMet competes with the inactivation by its dialdehyde. It has been verified in the case of the modified enzyme that the protection is afforded according to an equilibrium constant identical to that for tRNAfMet binding at the active site of the enzyme.Finally it is shown that the incorporation of one molecule of the dialdehyde of [14C]tRNA completely destroys the activity of the monomeric trypsin‐modified methionyl‐tRNA synthetase.