Phosphagen

Phosphagens, also known as macroergic compounds, are energy storage compounds, also known as high-energy phosphate compounds, chiefly found in muscular tissue in animals. They allow a high-energy phosphate pool to be maintained in a concentration range, which, if it all were ATP, would create problems due to the ATP consuming reactions in these tissues. As muscle tissues can have sudden demands for lots of energy; these compounds can maintain a reserve of high-energy phosphates that can be used as needed, to provide the energy that could not be immediately supplied by glycolysis or oxidative phosphorylation. Phosphagens supply immediate but limited energy.

The actual biomolecule used as a phosphagen is dependent on the organism. The majority of animals use arginine as phosphagen; however, the phylum Chordata (i.e., animals with spinal cords) use creatine. Creatine phosphate, or phosphocreatine, is made from ATP by the enzyme creatine kinase in a reversible reaction:

• Creatine + ATP $\leftrightarrow$ creatine phosphate + ADP (this reaction is Mg⁺⁺-dependent)

However, annelids (segmented worms) use a set of unique phosphagens; for example, earthworms use the compound lombricine.

Phosphagens were discovered by Dr Philip Eggleton FRSE and his wife Grace Eggleton.

Further reading

• Ellington, W Ross (2001). "EVOLUTION ANDPHYSIOLOGICALROLES OF PHOSPHAGENSYSTEMS". Annual Review of Physiology. 63 (1): 289–325. doi:10.1146/annurev.physiol.63.1.289. ISSN 0066-4278.
• Eggleton, Philip; Eggleton, Grace Palmer (1927). "The physiological significance of "phosphagen"". Journal of Physiology. 63 (2): 155–161. PMC 1514923.
• Eggleton, Philip; Eggleton, Grace Palmer (1928). "Further observations on phosphagen". Journal of Physiology. 65 (1): 15–24. PMC 1515019.
• Baldwin, Ernest (1933). "PHOSPHAGEN". Biological Reviews. 8 (1): 74–105. doi:10.1111/j.1469-185X.1933.tb01088.x. ISSN 1464-7931.