Monomeric structure of glutamyl-tRNA synthetase in Escherichia coli.

An investigation of the subunit structure of glutamyl-tRNA synthetase (EC 6.1.1.17) from Escherichia coli indicates that this enzyme is a monomer. The enzyme purified to apparent homogeneity is a single polypeptide chain with a molecular weight of 62,000 ± 3,000 and K^Glu_m ? 50 μM in the aminoacylation reaction. Analytical gel electrophoretic procedures were used to determine the molecular weight of species exhibiting glutamyl-tRNA synthetase activity in freshly prepared extracts of several strains of E. coli, which had been grown under various nutritional conditions and harvested at different stages of growth. In all cases, glutamyl-tRNA synthetase activity was associated with a protein having about the same molecular weight and K^Glu_m as the purified enzyme. Thus, no evidence of an oligomeric form of glutamyl-tRNA synthetase with a greater affinity for l-glutamate was obtained, in contrast to a previous report of J. Lapointe and D. Söll (J. Biol. Chem.247, 4966–4974, 1972).