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Adenylylation
Adenylylation,〔〔 now known as AMPylation, is a process in which adenosine monophosphate (AMP) molecule is covalently attached to a protein side chain, altering the function of the protein.〔 This covalent addition of AMP to a hydroxyl side chain of the protein is posttranslational modification that is stable and reversible.〔 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). This process can occur to molecules such as tyrosine residues. Enzymes that are capable of catalyzing this process are called AMPylators.
== Function ==
Similar to serine, threonine or tyrosine phosphorylation, AMPylation regulates the activity of some proteins, such as glutamine synthetase.〔 Additionally, AMPylation aids in allowing thermodynamically unfavorable overall reactions to take place by generating a leaving group in chemical mechanisms that indirectly use energy from ATP hydrolysis.〔 Unstable carboxylate-phosphate mixed anhydrides or of phosphoramidates are generated in this transient adenylyation reaction〔
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.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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