CKM, also known as CK-MM, is mainly expressed in skeletal muscle. As the primary CK isoenzyme, it also can be detected in heart muscle. CKM is a subunit of creatine kinase (CK). CK is an enzyme expressed by various tissues and cell types. It catalyses the conversion of creatine and consumes adenosine triphosphate (ATP) to create phosphocreatine and adenosine diphosphate (ADP). In the cells, the cytosolic CK enzymes consist of two subunits, which can be either B (brain type) or M (muscle type).