Creatine Kinase Enzyme System
The body's CK system is one of a number of unique systems responsible for providing energy to living cells. Comprised of creatine kinase (CK) and its substrates creatine and phosphocreatine, the CK system is responsible for cellular energy storage and transport between sites of energy production and sites of energy consumption. Specifically, the CK system is designed to deliver energy to those tissues that have sudden and/or high energy demands such as skeletal muscles, the heart, the brain, and various skin tissues.
How the system works
Creatine is a naturally occurring compound that is produced by the liver from arginine and glycine. It is predominantly found in the cells that make up the skeletal muscles, the heart, the brain, the retina, and various skin tissues.
Inside these cells, creatine is actively transported from the cytoplast into the mitochondria, which is also referred to as "the powerhouse of the cell." As creatine enters the mitochondria, the CK enzyme adds a phosphate group (Pi) to creatine, converting it into phosphocreatine (PCr), which is then stored inside the mitochondria for use at a later time. When energy production is required, PCr relinquishes its phosphate group to adenosine diphosphate (ADP), which is then transformed into adenosine triphosphate (ATP). ATP, the basic energy source of the human body, then exits the mitochondria and is used to satisfy the immediate energy needs of the cell.
Once the energy stored in ATP has been released, it returns to the mitochondria as ADP. Conversely, once phosphocreatine gives up the phosphate group to ADP it exits the mitochondria as creatine. Excess creatine is then broken down into creatinine, a waste product, which is processed by the kidneys and excreted in the urine.
In order to satisfy normal energy needs, the human body requires approximately two grams of creatine per day. However, the typical daily diet only provides the body with up to one gram of creatine. Accordingly, creatine supplementation is able to increase the body's level of creatine and phosphocreatine, which in turn increases ATP (energy) levels.
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