Creatine kinase

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Creatine kinase (CK), also known as phosphocreatine kinase or creatine phosphokinase (CPK) is an enzyme (EC 2.7.3.2) expressed by various tissue types. It catalyses the conversion of creatine to phosphocreatine, consuming adenosine triphosphate (ATP) and generating adenosine diphosphate (ADP).

In tissues that consume ATP rapidly, especially skeletal muscle, but also brain and smooth muscle, phosphocreatine serves as an energy reservoir for the rapid regeneration of ATP. Thus Creatine Kinase is an important enzyme in such tissues.

Clinically, creatine kinase is assayed in blood tests as a marker of myocardial infarction (heart attack), rhabdomyolysis (severe muscle breakdown), muscular dystrophy and in acute renal failure.

There are three different isoenzymes that come from three distinct locations in the body:

• BB: Brain, prostate, gastrointestinal, breast, ovary, lung
• MM: Skeletal muscle
• MB: Heart

Types

In most of the cell, the CK enzyme consists of two subunits, which can be either B (brain type) or M (muscle type). There are, therefore, three different isoenzymes: CK-MM, CK-BB and CK-MB. The genes for these subunits are located on different chromosomes: B on 14q32 and M on 19q13. In addition to those, there are two mitochondrial creatine kinases, the ubiquitous and sarcomeric form.

creatine kinase, brain
Identifiers
Symbol	CKB
Alt. Symbols	CKBB, CK-1
Entrez	1152
HUGO	1991
OMIM	123280
RefSeq	NM_001823
UniProt	P12277
Other data
EC number	2.7.3.2
Locus	Chr. 14 q32.3

Image:Creatine kinase.PNG
creatine kinase, muscle
Identifiers
Symbol	CKM
Alt. Symbols	CKMM, CK-3
Entrez	1158
HUGO	1994
OMIM	123310
RefSeq	NM_001824
UniProt	P06732
Other data
EC number	2.7.3.2
Locus	Chr. 19 q13.2-13.3

Isoenzyme patterns differ in tissues. CK-BB occurs mainly in tissues, and its levels do rarely have any significance in bloodstream. Skeletal muscle expresses CK-MM (98%) and low levels of CK-MB (1%). The myocardium (heart muscle), in contrast, expresses CK-MM at 70% and CK-MB at 25-30%. CK-BB is expressed in all tissues at low levels and has little clinical relevance.

The mitochondrial creatine kinase (CK_m), which produces ATP from ADP by converting creatine phosphate to creatine, is present between the two membranes of the mitochondrion. Apart from the mitochondrial form, there are three forms present in the cytosol—CK_a (in times of acute need, produces ATP in the cytosol at the cost of creatine phosphate), CK_c (maintains critical concentration of creatine and creatine phosphate in the cytosol by coupling their phosphorylation and dephosphorylation respectively with ATP and ADP) and CK_g (which couples direct phosphorylation of creatine to the glycolytic pathway (see glycolysis).

Laboratory testing

CK is often determined routinely in emergency patients. In addition, it is determined specifically in patients with chest pain and acute renal failure is suspected. Normal values are usually between 25 and 200 U/L. This test is not specific for the type of CK that is elevated.

Elevation of CK is an indication of damage to muscle. It is therefore indicative of injury, rhabdomyolysis, myocardial infarction, muscular dystrophy, myositis, myocarditis, malignant hyperthermia and neuroleptic malignant syndrome. It is also seen in McLeod syndrome and hypothyroidism. The use of statin medications, which are commonly used to decrease serum cholesterol levels, may be associated with elevation of the CPK level in about 1% of the patients taking these medications, and with actual muscle damage in a much smaller proportion.

Lowered CK can be an indication of alcoholic liver disease and rheumatoid arthritis.

Isoenzyme determination has been used extensively as an indication for myocardial damage in heart attacks. Troponin measurement has largely replaced this in many hospitals, although some centers still rely on CK-MB.

Differential Diagnosis

Differential Diagnosis of Increased Total CK

• Alcoholism
• Arterial embolism
• Bacterial myositis
• Becker's Muscular Dystrophy
• Crush injury or trauma
• Duchenne's Muscular Dystrophy
• Hyperthermia
• Hyperthyroidism
• Hypothyroidism
• Intramuscular injections
• Leyden-Moebius Muscular Dystrophy
• Liver, pancreas and gastrointestinal diseases
• Muscular spasm
• Myasthenia Gravis
• Myositis
• Neurogenic muscular atrophy
• Polymyositis
• Pregnancy and labor
• Rhabdomyolysis
• Seizure
• Surgery
• Thyrotoxicosis
• Vigorous exercise
• Viral myositis

Differential Diagnosis of Increased Total CK and CK-MB Ratio

• Cardiac contusion
• Cardiogenic shock
• Heart surgery
• Myocardial Infarction
• Perimyocarditis
• Right ventricular failure

See also

• reference ranges for common blood tests
• kinase

Additional images

Creatine

References

• Simply stated at mdausa.org
• MeSH Creatine+Kinase

v • d • e Phosphotransferases/kinases (EC 2.7)
2.7.1 - OH acceptor	Hexo- - Gluco- - Fructo- (Hepatic fructo-) - Galacto- - Phosphofructo- (1, 2) - Thymidine - NAD+ - Glycerol - Pantothenate - Mevalonate - Pyruvate - Deoxycytidine - PFP - Diacylglycerol - Bruton's tyrosine - Phosphoinositide 3 (Class I PI 3, Class II PI 3) - Sphingosine
2.7.2 - COOH acceptor	Phosphoglycerate - Aspartate
2.7.3 - N acceptor	Creatine
2.7.4 - PO4 acceptor	Phosphomevalonate - Adenylate - Nucleoside-diphosphate
2.7.6 - P2O7	Ribose-phosphate diphosphokinase - Thiamine pyrophosphokinase
2.7.7 - nucleotidyl-	Integrase - PNPase - Polymerase - RNase PH - UDP-glucose pyrophosphorylase - Galactose-1-phosphate uridylyltransferase -Terminal deoxynucleotidyl transferase - RNA replicase - Reverse transcriptase (Telomerase) - Transposase
2.7.8 - other phos.	N-acetylglucosamine-1-phosphate transferase
2.7.10-11 - protein	Tyrosine - Serine/threonine-specific

v • d • e Mitochondrial enzymes and transporters
Outer membrane	Long fatty acyl CoA synthetase - Kynureninase - Monoamine oxidase
Intermembrane space	Adenylate kinase - Creatine kinase
Inner membrane	Coenzyme Q - cytochrome c reductase -Cytochrome c - Dihydroorotate dehydrogenase -Glutamate aspartate transporter - Glycerol-3-phosphate dehydrogenase - NADH dehydrogenase - Succinate dehydrogenase
Matrix	Aconitase - Aspartate transaminase - ALDH2 - Carbamoyl phosphate synthase - Citrate synthase - Fumarase - Glutamate dehydrogenase - Isocitrate dehydrogenase - Malate dehydrogenase - Ornithine transcarbamoylase - Oxoglutarate dehydrogenase - Pyruvate dehydrogenase complex - Succinyl coenzyme A synthetase
Mitochondrial DNA	Complex I (7 units) - Complex III (1 unit) - Complex IV (3 units) - ATP synthase (2 units)

de:Creatin-Kinasefr:Créatine kinase

it:Creatinchinasi ja:クレアチンキナーゼ

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Acknowledgement and Attribution Regarding Sources of Content

Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .