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is a posttranslational modification
Posttranslational modification is the chemical modification of a protein after its translation. It is one of the later steps in protein biosynthesis, and thus gene expression, for many proteins....
that can occur to molecules such as tyrosine
Tyrosine or 4-hydroxyphenylalanine, is one of the 22 amino acids that are used by cells to synthesize proteins. Its codons are UAC and UAU. It is a non-essential amino acid with a polar side group...
residues. Adenylylation involves a phosphodiester bond
A phosphodiester bond is a group of strong covalent bonds between a phosphate group and two 5-carbon ring carbohydrates over two ester bonds. Phosphodiester bonds are central to all known life, as they make up the backbone of each helical strand of DNA...
between a hydroxyl group of the molecule undergoing adenylylation and the phosphate group of the adenosine monophosphate
Adenosine monophosphate , also known as 5'-adenylic acid, is a nucleotide that is used as a monomer in RNA. It is an ester of phosphoric acid and the nucleoside adenosine. AMP consists of a phosphate group, the sugar ribose, and the nucleobase adenine...
Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...
(i.e. adenylic acid).
The degree of adenylylation depends on the ratio of glutamine
Glutamine is one of the 20 amino acids encoded by the standard genetic code. It is not recognized as an essential amino acid but may become conditionally essential in certain situations, including intensive athletic training or certain gastrointestinal disorders...
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.