Evidence for significant quantities of creatine kinase MM isoenzyme in human brain

The isoenzymes of creatine kinase (ATP: creatine N-phosphotransferase, EC 2.7.3.2) in human brain were studied. Approx. 30% of total creatine kinase activity is due to the MM isoenzyme. The identity of this isoenzyme was confirmed by several techniques and shown not to be of mitochondrial origin.