AskDefine | Define creatine

Dictionary Definition

creatine n : an amino acid that does not occur in proteins but is found in the muscle tissue of vertebrates both in the free form and as phosphocreatine; supplies energy for muscle contraction [syn: creatin]

User Contributed Dictionary

English

Noun

  1. An amino acid 2-(carbamimidoyl-methyl- amino)acetic acid which naturally occurs in vertebrates and helps to supply energy to muscle and nerve cells

Usage notes

  • Not an α-amino acid

Extensive Definition

Creatine is nitrogenous organic acid that occurs naturally in vertebrates and helps to supply energy to muscle and nerve cells. Creatine was identified in 1832 when Derek Edward Bye discovered it as a component of skeletal muscle, which he later named creatine after the Greek word for flesh, Kreas.

Function

Creatine, by way of conversion to and from phosphocreatine, functions in all vertebrates and some invertebrates, in conjunction with the enzyme creatine kinase. A similar system based on arginine/phosphoarginine operates in many invertebrates via the action of Arginine Kinase. The presence of this energy buffer system keeps the ATP/ADP ratio high at subcellular places where ATP is needed, which ensures that the free energy of ATP remains high and minimizes the loss of adenosine nucleotides, which would cause cellular dysfunction. Such high-energy phosphate buffers in the form of phosphocreatine or phosphoarginine are known as phosphagens. In addition, due to the presence of subcompartmentalized Creatine Kinase Isoforms at specific sites of the cell, the phosphocreatine/creatine kinase system also acts as an intracellular energy transport system from those places where ATP is generated (mitochondria and glycolysis) to those places where energy is needed and used, e.g., at the myofibrils for muscle contraction, at the sarcoplasmic reticulum (SR) for calcium pumping, and at the sites of many more biological processes that depend on ATP.

Biosynthesis

In humans, about half of the daily creatine is biosynthesized from three different amino acids - arginine, glycine, and methionine. The rest is taken in by alimentary sources. Ninety-five percent of creatine is later stored in the skeletal muscles.
The enzyme GAMT (guanidinoacetate N-methyltransferase, also known as L-arginine:glycine amidinotransferase (AGAT), EC 2.1.4.1) is a mitochondrial enzyme responsible for catalyzing the first rate-limiting step of creatine biosynthesis, and is primarily expressed in the kidneys and pancreashttp://e-collection.ethbib.ethz.ch/ecol-pool/diss/fulltext/eth15180.pdf.
The second enzyme in the pathway (GAMT, guanidinoacetate N-methyltransferase, EC:2.1.1.2) is primarily expressed in the liver and pancreashttp://e-collection.ethbib.ethz.ch/ecol-pool/diss/fulltext/eth15180.pdf.
Genetic deficiencies in the creatine biosynthetic pathway lead to various severe neurological defectshttp://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=602360.

Controversy

While creatine's effectiveness in the treatment of many muscular, neuromuscular, and neuro-degenerative diseases is documented, its utility as a performance-enhancing food supplement in sports has been questioned (see creatine supplements for more information). Some have even proposed that its use as a performance enhancer should be banned. Despite this, creatine remains very popular.

Side effects

Short-term use of creatine in healthy individuals is generally considered safe (see Creatine supplements#Safety). Continuous intake of excessively high dosages of creatine may lead to any of several possible side effects. It has been hypothesized that consistently high doses could lead to hypertension due to increased water retention .
Creatine supplementation utilizing proper cycling and dosages, however, has not been linked with any adverse side effects beyond occasional dehydration due to increased muscular water uptake from the rest of the body.
According to the opinion statement of the European Food Safety Authorities (EFSA) published in 2004 it was concluded that "The safety and bioavailability of the requested source of creatine, creatine monohydrate in foods for particular nutritional uses, is not a matter of concern provided that there is adequate control of the purity of this source of creatine (minimum 99.95%) with respect to dicyandiamide and dihydro-1,3,5-triazine derivatives, as well as heavy metal contamination. The EFSA Panel endorses the previous opinion of the SCF that high loading doses (20 gram / day) of creatine should be avoided. Provided high purity creatine monohydrate is used in foods for particular nutritional uses, the Panel considers that the consumption of doses of up to 3g/day of supplemental creatine, similar to the daily turnover rate of creatine, is unlikely to pose any risk".
This opinion is corroborated by the fact that creatine is a natural component in mothers' milk and that creatine is absolutely necessary for brain development in the human embryo and the baby, as well as for optimal physiological functioning of the adult human body, especially the brain, nervous system, the muscles and other organs and cells of high energy expenditure, where the creatine kinase (CK) system is highly expressed and creatine levels are high.

Sources

In humans, approximately half of stored creatine originates from food (mainly from fresh meat and fish). Since vegetables do not contain creatine, vegetarians clearly show lower levels of muscle creatine which, upon creatine supplementation, rise to a level higher than in meat-eaters.

Creatine and the treatment of muscular diseases

Creatine supplementation has been, and continues to be, investigated as a possible therapeutic approach for the treatment of muscular, neuromuscular, neurological and neurodegenerative diseases (arthritis, congestive heart failure, Parkinson's disease, disuse atrophy, gyrate atrophy, McArdle's disease, Huntington's disease, miscellaneous neuromuscular diseases, mitochondrial diseases, muscular dystrophy, neuroprotection, etc.).
Two studies have indicated that creatine may be beneficial for neuromuscular disorders. First, a study demonstrated that creatine is twice as effective as the prescription drug riluzole in extending the lives of mice with the degenerative neural disease amyotrophic lateral sclerosis (ALS, or Lou Gehrig's disease). The neuroprotective effects of creatine in the mouse model of ALS may be due either to an increased availability of energy to injured nerve cells or to a blocking of the chemical pathway that leads to cell death.
Second, creatine has been demonstrated to cause modest increases in strength in people with a variety of neuromuscular disorders.
Third, creatine has been shown to be beneficial as an adjuvant treatment for several neuro-muscular and neuro-degenerative diseases (11,12) and its potential is just beginning to be explored in several multi-center clinical studies in the USA and elsewhere.

See also

References

External links

creatine in Czech: Kreatin
creatine in Danish: Kreatin
creatine in German: Kreatin
creatine in Spanish: Creatina
creatine in French: Créatine
creatine in Indonesian: Kreatin
creatine in Italian: Creatina
creatine in Hebrew: קראטין
creatine in Dutch: Creatine
creatine in Japanese: クレアチン
creatine in Polish: Kreatyna
creatine in Portuguese: Creatina
creatine in Russian: Креатин
creatine in Slovak: Kreatín
creatine in Finnish: Kreatiini
creatine in Swedish: Kreatin
creatine in Turkish: Kreatin
creatine in Chinese: 肌酸
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