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Phosphagen
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<p>Phosphagens, also known as macroergic compounds, are high energy storage compounds, also known as <a href="/facts/High-energy_phosphate/fwekhW32">high-energy phosphate</a> compounds, chiefly found in <a href="/facts/Muscle/dmxrL8pH">muscular</a> tissue in <a href="/facts/Animal/4b8J33nd">animals</a>. They allow a high-energy phosphate pool to be maintained in a concentration range, which, if it all were <a href="/facts/Adenosine_triphosphate/nB9bwgcU">adenosine triphosphate</a> (ATP), would create problems due to the ATP-consuming reactions in these tissues. As muscle tissues can have sudden demands for much 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 <a href="/facts/Glycolysis/a5ApxLoG">glycolysis</a> or <a href="/facts/Oxidative_phosphorylation/en2l08P9">oxidative phosphorylation</a>. Phosphagens supply immediate but limited energy. </p><p>The actual <a href="/facts/Biomolecule/DGvFzN7R">biomolecule</a> used as a phosphagen is dependent on the organism. The majority of animals use <a href="/facts/Arginine/y49Hdf1e">arginine</a> as phosphagen; however, the phylum <a href="/facts/Chordata/AldL6ARm">Chordata</a> (i.e., animals with spinal cords) use <a href="/facts/Creatine/xhBTBard">creatine</a>. <a href="/facts/Creatine_phosphate/CzG0fmUP">Creatine phosphate</a> (CP), or <a href="/facts/Creatine_phosphate/CzG0fmUP">phosphocreatine</a> (PCr), is made from ATP by the enzyme <a href="/facts/Creatine_kinase/kYtNQKjy">creatine kinase</a> in a reversible reaction: </p> <ul><li>Creatine + ATP ⇌ creatine phosphate + ADP + <a href="/facts/Hydron_(chemistry)/v5Qkumvm">H+</a> (this reaction is <a href="/facts/Magnesium_in_biology/ENuowoyY">Mg2+</a>-dependent)</li></ul> <p>However, <a href="/facts/Annelids/PQvb7NAM">annelids</a> (segmented worms) use a set of unique phosphagens; for example, earthworms use the compound <a href="/facts/Lombricine/gNCt7y5R">lombricine</a>. </p><p>Phosphagens were discovered by <a href="/facts/Philip_Eggleton/5ThvY0C8">Philip Eggleton</a> and his wife Grace Eggleton. </p>