Glu-tRNAGln amidotransferase or glutaminyl-tRNA synthase (glutamine-hydrolysing) enzyme is an amidotransferase that catalyzes the conversion of the non-cognate amino acid glutamyl-tRNAGln to the cognate glutaminyl-tRNAGln.. It catalyzes the reaction: This enzyme belongs to the family of ligases, specifically those forming carbon-nitrogen bonds carbon-nitrogen ligases with glutamine as amido-N-donor. The systematic name of this enzyme class is glutamyl-tRNAGln:L-glutamine amido-ligase (ADP-forming). This enzyme participates in glutamate metabolism and alanine and aspartate metabolism.

Function and evolutionary significance

Most bacterial and all archaea genomes do not encode a glutaminyl-tRNA synthetase (GlnRS). Instead they first synthesize the attachment of an amino acid on the tRNAGln by first attaching a non-cognate glutamate to the tRNA. Then these organisms use the amidotransferase: glutaminyl-tRNA synthase (glutamine-hydrolysing) enzyme to convert the glutamate attached to tRNAGln to glutamine.