Adenylylation

Adenylylation is a posttranslational modification that can occur to molecules such as tyrosine residues. Adenylylation involves a phosphodiester bond between a hydroxyl group of the molecule undergoing adenylylation and the phosphate group of the adenosine monophosphate nucleotide (i.e. adenylic acid).

The degree of adenylylation depends on the ratio of glutamine to α-ketoglutarate: The higher this ratio the more monomers are adenylylated, thereby producing lower activity of glutamine synthetase; the lower the ratio the less monomers are adenylated and the higher activity of glutamine synthetase. A high ratio is a sign of cellular nitrogen sufficiency, whereas a low ratio is evidence of a limited nitrogen and the need for ammonia fixation by glutamine synthetase.