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 ⇌ creatine phosphate + ADP (this reaction is Mg⁺⁺-dependent)

How is phosphocreatine produced?

Creatine phosphate can be obtained from two sources: ingestion of meat and internal production by the liver and kidneys. Creatine and creatinine (fromed from the metabolism of creatine) waste is removed from the body through the kidneys and urinary system.

What are the requirements for phosphagen to generate energy?

Phosphagen. This system uses creatine phosphate (CP) and has a very rapid rate of ATP production. The creatine phosphate is used to reconstitute ATP after it's broken down to release its energy. The total amount of CP and ATP stored in muscles is small, so there is limited energy available for muscular contraction.