Creatine is a nitrogenous organic acid that occurs naturally in vertebrates. Its main role is to facilitate recycling of adenosine triphosphate (ATP), the energy currency of the cell, primarily in muscle and brain tissue. This is achieved by recycling adenosine diphosphate (ADP) to ATP via donation of phosphate groups. Creatine also acts as a pH buffer in tissues.
Creatine synthesis primarily occurs in the liver and kidneys.On average, it is produced endogenously at an estimated rate of about 8.3 mmol or 1 gram per day in young adults.Creatine is also obtained through the diet at a rate of about 1 gram per day from an omnivorous diet. Most of the human body's total creatine and phosphocreatine stores are found in skeletal muscle, while the remainder is distributed in the blood, brain, and other tissues.
Creatine was identified in 1832 when Michel Eugène Chevreul isolated it from the basified water-extract of skeletal muscle. He later named the crystallized precipitate after the Greek word for meat, κρέας (kreas). In solution, creatine is in equilibrium with creatinine.Creatine is a derivative of the guanidinium cation.