Creatine phosphokinase, also known as creatine kinase (CK), is an enzyme expressed by various tissues and cell types. CK catalyses the conversion of creatine and consumes adenosine triphosphate (ATP) to create phosphocreatine and adenosine diphosphate (ADP). In cells, the "cytosolic" CK enzymes consist of two subunits, which can be either B (brain type) or M (muscle type). There are three different isoenzymes: CKMM, CKBB and CKMB. 2400-1986 recognises CKMB but does not distinguish between isoform CKMB1 and CKMB2. This antibody shows less than 0.1 % reactivity with CKBB or CKMM and minimal reactivity with other human serum proteins.