Mitochondrial CK (EC 2.7.3.2) in the human heart.

CKm, a mitochondrial form of CK, can be isolated from human cardiac muscle. It occurs in two forms, separable on the basis of the difference in net charge. Both molecules have a dimeric structure and consist of two identical subunits. Upon incubation in a human serum, the CK isozyme with the faster cathodal mobility is rapidly converted into the slower form, which has an isoelectric point of 6.94. This makes it impossible to separate this slow CKM form from CK MM (isoelectric point: 6.86) by means of any method that separates on a basis of differences in net charge. Furthermore the two molecules have an almost identical molecular weight. The only difference between the two molecules we have been able to detect is the different behaviour against anti-M antibodies.