Mitochondrial creatine kinase (EC 2.7.3.2) in the brain.

No CK MM was found in human brain tissue. Both human and rat brain tissue, however, contain a non MM, non BB CK isozyme. The protein is membrane bound. Evidence is presented that it is a mitochondrial variant of the enzyme. This mitochondrial brain CK occurs in two forms. Both a low molecular mass form (Mr = 65,000) and a high molecular mass form are detectable. The isoelectric point of the low molecular mass form, Br-CKm1, is similar to the isoelectric point of CK MM. Complications may arise when techniques are used that try to separate the mitochondrial CK forms from CK MM on basis of differences in net change. The two mitochondrial brain CK forms are called Br-CKm1 and Br-CKm2. Whether these two enzymes are identical to the mitochondrial heart CK forms remains unclear.