The muscle creatine occurs mainly in the form of phosphocreatine, which is
the main source of energy for contracting muscle fibres. It belongs to one of the
eight phosphagenes occurring in animals and has its own enzyme creatine kinase
(EC 2.7.3.2), discovered by Lohman in 1934. This is a key enzyme that controls the
energy economy of the cell. Creatine kinase is also essential for the effective operation
of pumps including calcium, providing calcium homeostasis in activated muscle
cells (Grzyb and Skorkowski, 2008).