Etude de la méthionyl tRNA synthétase de Escherichia coli

Treatment of partially purified methionyl tRNA synthetase from Escherichia coli B (E. coli B) with p‐hydroxymercuribenzoate (pHMB) leads to loss of the capacity to form methionly adenylate and methionyl tRNA. Inactivation of the capacity to activate methionine could not be reversed by the addition of GSH or 2‐mercaptoethanol. The Presence of low concentrations of l‐methioninyl adenylate (a structural analog of methionyl adenylate) during pHMB‐treatment, results in complete and selective protection of the active site responsible for the activation of methionine. Under these conditions, the addition of 2‐mercaptoethanol leads to full recovery of the capacity to charge tRNA. The enzyme which has lost the capacity to form methionyl tRNA as a result of pHMB‐treatment in the presence of methioninyl adenylate, has the same elution characteristics as untreated enzyme when examined by gel filtration through Sephadex G‐200. It is concluded that loss of the capacity to charge tRNA is not a consequence of dissociation of the enzyme into subunits. These results provide a clear‐cut distinction between the active site responsible for the activation of the amino acid, and the site(s) involved in the formation of aminoacyl tRNA, in the case of methionyl tRNA synthetase.