Human creatine kinase. Isoenzymes and logistics of energy distribution.

A simple procedure to estimate creatine kinase of mitochondrial origin (CK-mit) was tested in homogenates from human myocardial and skeletal muscle. Thereafter CK-mit was estimated as the difference between the activity remaining after immunoinhibition with anit-CK-M and chromatographic isolation of CK-MB. This method was applied to selected human myocardial and skeletal muscle biopsies. These biopsies were selected on the basis of citrate synthetase activity so as to give a large range in oxidative capacity. CK-MB and CK-mit were correlated and both CK-MB and CK-mit correlated to citrate synthetase activity. The isoenzymes CK-MB and CK-mit were thus associated with the oxidative capacity of the tissue. The results confirm the energy shuttle hypothesis for CK with CK-MB located at target organelles.