Glutamyl-tRNA synthetases from wheat. Isolation and characterization of three dimeric enzymes

Three dimeric glutamyl-tRNA synthetases (GluRS) were isolated from extracts of quiescent wheat germ and wheat chloroplasts. The chloroplast enzyme (Mr = 110 000), called GluRS C, exhibits a prokaryotic (Escherichia coli) tRNA specificity. Two enzymes were found in the quiescent germ and were separated on phosphocellulose P11: one called GluRS P, probably the mitochondrial enzyme, has the same tRNA specificity as GluRS C; the other, called GluRS E, has eukaryotic (wheat germ) tRNA specificity. Both enzymes exhibit a molecular weight close to 160 000. Each of these enzymes co-eluate on hydroxyapatite and phosphocellulose chromatographies with an unstable active monomer whose molecular weight is approximately half that of the corresponding dimer. Two assumptions are discussed about these monomers.