InterPro: IPR000749 ATP:guanido phosphotransferase

ATP:guanido phosphotransferases are a family of structurally and functionally related enzymes [1, 2] that reversibly catalyse the transfer of phosphate between ATP and various phosphogens. The enzymes belonging to this family include:

• Glycocyamine kinase (EC:2.7.3.1), which catalyses the transfer of phosphate from ATP to guanidoacetate.
• Arginine kinase (EC:2.7.3.3), which catalyses the transfer of phosphate from ATP to arginine.
• Taurocyamine kinase (EC:2.7.3.4), an annelid-specific enzyme that catalyses the transfer of phosphate from ATP to taurocyamine.
• Lombricine kinase (EC:2.7.3.5), an annelid-specific enzyme that catalyses the transfer of phosphate from ATP to lombricine.
• Smc74, a cercaria-specific enzyme from Schistosoma mansoni [1].
• Creatine kinase (EC:2.7.3.2) (CK) [3, 4], which catalyses the reversible transfer of high energy phosphate from ATP to creatine, generating phosphocreatine and ADP.

Creatine kinase plays an important role in energy metabolism of vertebrates. There are at least four different, but very closely related, forms of CK. Two isozymes, M (muscle) and B (brain), are cytosolic, while the other two are mitochondrial. In sea urchins there is a flagellar isozyme, which consists of the triplication of a CK-domain. A cysteine residue is implicated in the catalytic activity of these enzymes and the region around this active site residue is highly conserved.