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.