Types
In the cells, the "cytosolic" CK enzymes consist 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 three cytosolic CK isoforms, there are two mitochondrial creatine kinase isoenzymes, the ubiquitous and sarcomeric form. The functional entity of the latter two mitochondrial CK isoforms is an octamer consisting of four dimers each.
While mitochondrial creatine kinase is directly involved in formation of phospho-creatine from mitochondrial ATP, cytosolic CK regenerate ATP from ADP, using PCr. This happens at intracellular sites where ATP is used in the cell, with CK acting as an in situ ATP regenerator.
| gene | protein |
|---|---|
| CKB | creatine kinase, brain, BB-CK |
| CKBE | creatine kinase, ectopic expression |
| CKM | creatine kinase, muscle, MM-CK |
| CKMT1A, CKMT1B | creatine kinase mitochondrial 1; ubiquitous mtCK; or umtCK |
| CKMT2 | creatine kinase mitochondrial 2; sarcomeric mtCK; or smtCK |
Isoenzyme patterns differ in tissues. CK-BB is expressed in all tissues at low levels and has little clinical relevance. 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%.
Read more about this topic: Creatine Kinase
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