title: The monomeric glutamyl-tRNA synthetase of Escherichia coli. Purification and relation between its structural and catalytic properties.
abstract: The glutamyl-tRNA synthetase has been purified to homogeneity from Escherichia coli with a yield of about 50%. It is a monomer with a molecular weight of 56,000 and has the same kinetic properties as those of the alpha chain of the dimeric alphabeta-glutamyl-tRNA synthetase described previously (Lapointe, J., and Söll, D. (1972) J. Biol. Chem. 247, 4966-4974). It is the smallest amino-acyl-tRNA synthetase purified from E. coli and contains no important sequence repetition. It is also the only monomeric aminoacyl-tRNA synthetase reported so far to contain no major sequence duplication. Considering its structural and mechanistic similarities with the glutaminyl- and the arginyl-tRNA synthetases of E. coli, we propose the existence of a relation between the true monomeric character of the glutamyl-tRNA synthetase (as opposed to monomers with sequence duplications) and its requirement for tRNA in the activation of glutamate. A single sulfhydryl group of the native enzyme reacts with 5,5'-dithiobis(2-nitrobenzoic acid) causing no loss of enzymatic activity, whereas four such groups per enzyme react in the presence of 4 M guanidine HCl.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000604:Amino Acyl-tRNA Synthetases / Q000378:metabolism*; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology; D004926:Escherichia coli / Q000201:enzymology*; D005975:Glutamate-tRNA Ligase / Q000302:isolation & purification / Q000378:metabolism*; D006902:Hydroxymercuribenzoates / Q000494:pharmacology; D007700:Kinetics; D008970:Molecular Weight; D010446:Peptide Fragments / Q000032:analysis
chemical_list: D000596:Amino Acids; D006902:Hydroxymercuribenzoates; D010446:Peptide Fragments; D004228:Dithionitrobenzoic Acid; D000604:Amino Acyl-tRNA Synthetases; D005975:Glutamate-tRNA Ligase