fosfagens

Fosfagens, also known as phosphagens, are high-energy phosphate compounds that function as cellular energy buffers. They store phosphate groups in a readily mobilizable form and rapidly regenerate ATP when energy demand spikes, particularly in tissues with rapid and intermittent energy use such as skeletal muscle and brain.

The most widely known phosphagen in vertebrates is creatine phosphate (phosphocreatine). In many invertebrates, arginine phosphate is the dominant form. Other phosphagens, such as lombricine phosphate or taurocyamine phosphate, occur in specific groups of animals. The phosphagen pool is maintained by tissue-specific kinases and is replenished as needed.

Mechanism: When ATP is consumed for muscle contraction or other processes, the phosphagen donates a phosphate to ADP to reform ATP, catalyzed by creatine kinase in vertebrates or arginine kinase in invertebrates. This reaction provides a rapid but short-lived boost of ATP for seconds of high-intensity activity, bridging the gap until oxidative phosphorylation or glycolysis can meet demand.

Regeneration and synthesis: Phosphocreatine is replenished by the transfer of a phosphate from ATP to creatine, typically during recovery, using mitochondrial ATP. Creatine is synthesized mainly in the liver and kidney from glycine, arginine, and methionine. Arginine phosphate pools are restored by arginine kinase in taxa that express it.

Significance: The phosphagen system is an evolutionarily conserved mechanism for rapid energy supply and is a focus in exercise physiology and muscle pathology. Creatine kinase activity and phosphagen levels are commonly measured to assess muscle energy state and tissue integrity.