CK-MB: a valuable test?

Abstract

ATP:creatine N-phosphotransferase, EC 2.7.32., trivial name creatine kinase (CK), reversibly catalyses the transfer of a highenergy phosphate bond from ATP to creatine. It is found in high concentrations in skeletal tongue, diaphragm, heart and and in much lower concentrations in kidney, lung and liver. Like other enzymes of clinical interest, isoenzymes exist. Thus, Burger et al.! and Burger, Richterich and Aebf described three forms MM, MB and BB. Dawson, Eppenberger and Kaplan;' by hybridisation experiments, were able to confirm the predictable dimeric structure and they and Yue et al. demonstrated that there were two active sites per CK molecule, one which binds creatine and phosphocreatine and the other ATP and ADP. van der Veen and Willebrands reported that skeletal muscle contained virtually only MM, brain only BB and myocardium both MM and MB. These findings have been in general confirmed by many other workers, but MB, initially thought to be cardiospecific, has subsequently been demonstrated in other tissues, e.g. skeletal muscle, brain, gut, bladder, lung, liver! and uterus. However, interpretation of these results is difficult because of the different types of method of assay, different types of specimen (autopsy, biopsy), different methods of homogenisation, and different methods of storage that have been used. In addition to the cytosolic isoenzymes, a mitochondrial isoenzyme, I I CK m , of which there are probably two forms, has been demonstrated by various workers in brain and cerebrospinal fluid. Electrophoretically, it moves with MM. In serum, 'macro CK' has also been demonstrated and is thought to be a