Reversibly catalyzes the transfer of phosphate between ATP and various phosphogens (e.g. creatine phosphate). Creatine kinase isoenzymes play a central role in energy transduction in tissues with large, fluctuating energy demands, such as skeletal muscle, heart, brain and spermatozoa. The isoform-specific function of B creatine kinase may be to provide a system for the rapid regeneration of metabolic energy for sodium transport. ATP + creatine = ADP + H(+) + N-phosphocreatine Dimer of identical or non-identical chains. With MM being the major form in skeletal muscle and myocardium, MB existing in myocardium, and BB existing in many tissues, especially brain. Basal membrane of the sodium chloride-secreting epithelia. Creatine kinase B is the major isoform present in the rectal gland. Belongs to the ATP:guanido phosphotransferase family.