Glutamol adenylate10was a competitive inhibitor (Ki= 3 μM) of glutamyl-tRNA synthetase fromEscherichia coli. TheN6-benzoyl adenine derivative9was also an inhibitor (Ki∼ 60 μM). Replacement of adenine by other bases (purine, cytosine, dihydrocytosine, uridine) resulted in a more than 1000-fold loss in activity, indicating the important contribution of the adenine ring to the enzyme binding.