CKBB, also named as B-CK and CKB, is a member of the ATP:guanido phosphotransferase protein family. It is a cytoplasmic enzyme involved in energy homeostasis. CKBB reversibly catalyzes the transfer of phosphate between ATP and various phosphogens such as creatine phosphate. It acts as a homodimer in brain as well as in other tissues, and as a heterodimer with a similar muscle isozyme in heart. CK isoenzymes play a central role in energy transduction in tissues with large, fluctuating energy demands, such as skeletal muscle, heart, brain and spermatozoa. CK MB consists of a dimer of nonidentical chains. With MM being the major form in skeletal muscle and myocardium, MB existing in myocardium, and BB existing in many tissues, especially brain.