What is creatine phosphate anatomy
By Daniel Kim
Function and chemistry of Phosphocreatine
The muscles of the body function through the use of ATP, or adenosine triphosphate, to power contractions. When one molecule of ATP is used in the contraction process, it is hydrolyzed to ADP, adenosine diphosphate, and an inorganic phosphate. The muscles’ limited ATP supply is used very quickly in muscle activity, so the need to regenerate ATP is essential. One of the ways that this ATP supply is regenerated is through the molecule creatine phosphate (or phosphocreatine). In the process of regeneration of ATP, creatine phosphate transfers a high-energy phosphate to ADP. The products of this reaction are ATP and creatine. 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.
Advantages and Disadvantages of Creatine
Advantages:
The supplementation of creatine phosphate has been shown in studies to be effective for many people. With supplementation, muscle mass, explosive power, and strength have been shown to increase in most cases. Thus, for activities that require short bursts of energy such as football and sprinting, creatine phosphate has improved athletic performance. Another advantage to taking creatine phosphate is that it is a legal substance in most athletic competitions, such as the Olympics and professional athletics. In addition, creatine phosphate is not considered a drug by the FDA.
Disadvantages:
In regard to health, the major disadvantage to supplimenting with creatine phosphate is that no long term studies have been done on the effects. Some scientists speculate that with supplimentation, the body could stop naturally producing creatine. Also, the effects of the increased waste products of creatine and creatinine on the kidneys are a concern. Supporting this claim, the creatine content of urine with supplimentation is 90 times greater than normal. Other reported side effects include nausea, gastrointestinal disturbances, and increased muscle cramping. Another major disadvantage to phosphocreatine is that it is only effective for short bursts of energy. This is because ATP is regenerated using different methods during long term activity. Therefore, increased levels of phosphocreatine would be useless for an athelete such as a marathon runner.
creatine phosphate
phos•pho•cre•a•tine
(ˌfɒs foʊˈkri əˌtin, -tɪn)
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Identification
Phosphocreatine is a cardioprotective agent indicated for use in cardiac surgery.
Generic Name Phosphocreatine DrugBank Accession Number DB13191 Background
Phosphocreatine – or creatine phosphate – is the phosphorylated form of creatine. It is primarily found endogenously in the skeletal muscles of vertebrates where it serves a critical role as a rapidly acting energy buffer for muscle cell actions like contractions via its ability to regenerate adenosine triphosphate (ATP) from adenosine diphosphate (ADP).
Type Small Molecule Groups Nutraceutical Structure
Structure for Phosphocreatine (DB13191)
Pharmacology
Phosphocreatine is a naturally occuring substance that is found predominantly in the skeletal muscles of vertebrates. Its primary utility within the body is to serve in the maintanence and recycling of adenosine triphosphate (ATP) for muscular activity like contractions.
Given this utility of phosphocreatine to recycle ATP, the most plausible therapeutic potentials for its use involve conditions caused by energy shortage or by increased energy requirements – such as in ischemic stroke and other cerebrovascular diseases. It is important to note however that relatively little clinical research has been done to significantly further the evidence for any such indications, although it is administered intravenously for cardiovascular conditions in some countries.
Additionally, because phosphocreatine is not regulated as a controlled substance it is taken as a supplement by some professional athletes as a means to perhaps increase short bursts of muscle strength or energy for professional athletics.
Creatine is a naturally occurring chemical within the body and is primarily stored in skeletal muscle in both free and phosphorylated forms. Phosphocreatine is the name given to the phosphorylated form of creatine. Additionally, phosphocreatine can also be found in other areas of the body like the kidneys, liver, and brain. In fact, most in vivo synthesis of creatine occurs in the liver where amidine groups from arginine are transfered to glycine with the help of the glycine transaminidase enzyme to form guanidinoacetic acid. This acid is then methylated with the methyl group of S-adenosylmethionine via guanidinoacetate methyltransferase to generate creatine. The synthesized creatine is transported to storage sites in skeletal muscle via the bloodstream.
The phosphorylation of creatine is reversible in both a forwards and backwards reaction. That is, while phosphocreatine is capable of anaerobically donating a phosphate group to adenosine diphosphate (ADP) to regenerate ATP, at the same time excess ATP can be dephosphorylated during periods of low muscle activity to convert creatine to phosphocreatine. This dual activity in synthesizing phosphocreatine from excess levels of ATP during rest and use of phosphocreatine to regenerate ATP during high activity demonstrates the crucial utility of phosphocreatine in acting as an energy buffer in body mucle cells.
Phosphocreatine’s fast regeneration of ATP is considered a coupled reaction – in essence, the energy released from transferring a donating a phosphate group from phosphocreatine is used to regenerate ATP. Phosphocreatine consequently plays an essential role in body tissues that have high, fluctuating energy requirments like muscle and brain tissues.
Mechanism of action
Adenosine triphosphate (ATP) is the primary source of chemical energy that body muscles use to perform contractions. During such contraction processes, ATP molecules are depleted as they undergo hydrolysis reactions and become adenosine diphosphate (ADP). To maintain homeostasis in muscle activity, the ATP supply of muscles must be regenerated regularly.
Phosphocreatine occurs naturally within the body and is capable of regenerating ATP by transferring a high-energy phosphate from itself to ADP, resulting in the formation of ATP and creatine. This kind of regeneration of ATP with phosphocreatine typically occurs within seconds of intense muscular or neuronal effort, acting as a quickly accessible reserve of high-energy phosphates for the recycling of ATP in body muscle tissues. ATP recycling from phosphocreatine is in fact known as the quickest form of ATP regeneration.
Learning Objectives
Describe the types of skeletal muscle fibers
By the end of this section, you will be able to:
- Differentiate between slow oxidative fibers, fast oxidative fibers, and fast glycolytic fibers
Skeletal muscle fibers can be classified based on two criteria: 1) how fast do fibers contract relative to others, and 2) how do fibers regenerate ATP. Using these criteria, there are three main types of skeletal muscle fibers recognized (Table 1). Slow oxidative (SO) fibers contract relatively slowly and use aerobic respiration (oxygen and glucose) to produce ATP. Fast oxidative (FO) fibers have relatively fast contractions and primarily use aerobic respiration to generate ATP. Lastly, fast glycolytic (FG) fibers have relatively fast contractions and primarily use anaerobic glycolysis. Most skeletal muscles in a human body contain all three types, although in varying proportions.
The speed of contraction is dependent on how quickly myosin’s ATPase hydrolyzes ATP to produce cross-bridge action. Fast fibers hydrolyze ATP approximately twice as rapidly as slow fibers, resulting in much quicker cross-bridge cycling (which pulls the thin filaments toward the center of the sarcomeres at a faster rate).
The primary metabolic pathway used by a muscle fiber determines whether the fiber is classified as oxidative or glycolytic. If a fiber primarily produces ATP through aerobic pathways, then it is classified as oxidative. More ATP can be produced during each metabolic cycle, making the fiber more resistant to fatigue. Glycolytic fibers primarily create ATP through anaerobic glycolysis, which produces less ATP per cycle. As a result, glycolytic fibers fatigue at a quicker rate.
Slow oxidative fibers have structural elements that maximize their ability to generate ATP through aerobic metabolism. These fibers contain many more mitochondria than the glycolytic fibers, as aerobic metabolism, which uses oxygen (O2) in the metabolic pathway, occurs in the mitochondria. This allows slow oxidative fibers to contract for longer periods because of the large amount of ATP they can produce, but they have a relatively small diameter and thus do not produce a large amount of tension.
In addition to increased numbers of mitochondria, slow oxidative fibers are extensively supplied with blood capillaries to supply O2 from the bloodstream. They also possess myoglobin, an O2-binding molecule similar to hemoglobin in the red blood cells. The myoglobin stores some of the needed O2 within the fibers themselves and is partially responsible for giving oxidative fibers a dark red color.
The ability of slow oxidative fibers to function for long periods without fatiguing makes them useful in maintaining posture, producing isometric contractions, and stabilizing bones and joints. Because they do not produce high tension, they are not used for powerful, fast movements that require high amounts of energy and rapid cross-bridge cycling.
Fast glycolytic fibers primarily use anaerobic glycolysis as their ATP source. They have a large diameter and possess large volumes of glycogen which is used in glycolysis to generate ATP quickly. Because of their reliance on anaerobic metabolism, these fibers do not possess substantial numbers of mitochondria, a limited capillary supply, or significant amounts of myoglobin, resulting in a white coloration for muscles containing large numbers of these fibers.
Fast glycolytic fibers fatigue quickly, permitting them to only be used for short periods. However, during these short periods, the fibers are able to produce rapid, forceful contractions associated with quick, powerful movements.
Fast oxidative fibers are sometimes called intermediate fibers because they possess characteristics that are intermediate between slow oxidative fibers and fast glycolytic fibers. These fibers produce ATP relatively quickly, and thus can produce relatively high amounts of tension, but because they are oxidative, they do not fatigue quickly. Fast oxidative fibers are used primarily for movements, such as walking, that require more energy than postural control but less energy than an explosive movement.
Chapter Review
The three types of muscle fibers are slow oxidative (SO), fast oxidative (FO) and fast glycolytic (FG). Slow oxidative fibers use aerobic metabolism to produce low power contractions over long periods and are slow to fatigue. Fast oxidative fibers use aerobic metabolism to produce ATP but produce higher tension contractions than slow oxidative fibers. Fast glycolytic fibers use anaerobic metabolism to produce powerful, high-tension contractions but fatigue quickly.
