Arginine kinase

 ( Ec 2.7.3 ) 

In enzymology, arginine kinase () is an enzyme that catalysis the chemical reaction

ATP + L-arginine $\backslash rightleftharpoons$ ADP + N^ω-phospho-L-arginine

Thus, the two substrates of this enzyme are ATP and L-arginine, whereas its two products are ADP and N^ω-phospho-L-arginine. Unlike the phosphoester bond, formed during the phosphorylation of serine, threonine or tyrosine residues, the phosphoramidate (P-N bond) in phospho-arginine is unstable at low pH (<8), making it difficult to detect with the traditional mass spectrometry protocols.

Arginine kinase belongs to the family of , specifically those transferring phosphorus-containing groups (phosphotransferases) with a nitrogenous group as acceptor. This enzyme participates in arginine and proline metabolism.

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Nomenclature The systematic name of this enzyme class is

• ATP:L-arginine N^ω-phosphotransferase

Other names in common use include

• arginine phosphokinase,
• adenosine 5'-triphosphate: L-arginine phosphotransferase,
• adenosine 5'-triphosphate-arginine phosphotransferase,
• ATP:L-arginine N-phosphotransferasel ATP:L-arginine, and
• ω-N-phosphotransferase.

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Function In Gram-positive bacteria, such as Bacillus subtilis, the arginine kinase McsB phosphorylates the arginine residues on incorrectly folded or aggregated proteins to target them for degradation by the bacterial protease ClpC-ClpP (ClpCP).The phospho-arginine (pArg) modification is recognised by the N-terminal domain of ClpC, the protein-unfolding subunit of the ClpCP protease. Following recognition, the target protein is degraded by the ClpP subunit which has protease activity. Since phosphorylation reverses arginine's charge, the pArg modification has an unfolding effect on the target protein, easing its proteolytic degradation. Arginine phosphorylation is a dynamic post-translational modification, which can also be reversed by pArg-specific phosphatases, such as the bacterial YwlE. The pArg-ClpCP mechanism for protein degradation in bacteria is analogous to the eukaryotic ubiquitin-proteasome system.

Several studies have reported the presence of arginine kinases in eukaryotes. A recent study identified arginine phosphorylation on 118 proteins in Jurkat cells, which were primarily proteins with DNA/RNA-binding activities. The function of arginine phosphorylation in eukaryotes however is still unknown.

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Arginine kinase as an allergen Recent research has identified arginine kinase as a major panallergen in invertebrates, including edible insects such as the yellow mealworm (*Tenebrio molitor*). This enzyme can act as an IgE-binding allergen, and sensitization to arginine kinase may result in allergic reactions in individuals already sensitized to homologous proteins from other arthropods (e.g., crustaceans, mites). Cross-reactivity mediated by IgE antibodies has been observed between arginine kinase from edible insects and allergens in shrimp and house dust mites, which means clinical reactions may occur even upon first exposure. The emergence of edible insects in the human diet highlights the importance of arginine kinase in assessing the allergenic risks of novel food proteins.

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Structural studies As of late 2007, 8 structures have been solved for this class of enzymes, with PDB accession codes , , , , , , , and .

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Further reading

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