Macro creatine kinases: results of isoenzyme electrophoresis and differentiation of the immunoglobulin-bound type by radioassay.

In 2.9% of sera from 1253 unselected patients we detected two different types of macromolecular creatine kinases (CK; EC 2.7.3.2). One macro type was represented by immunoglobulin-linked CK: in sera containing macro CK-BB isoenzyme, 125I-labeled CK-BB was bound with high affinity to the immunoglobulin fraction. Furthermore, during electrophoresis, macro CK-BB mostly migrated between CK-MB and CK-MM, and was fixed to Protein A from Staphylococcus aureus. We therefore propose radioelectrophoresis as a specific, highly sensitive, and simple method for detecting this type of macro CK. This form occurs predominantly in elderly women, is not correlated to any specific disease, and persists in blood over a long period of time. In contrast, a second type (macro-CK type 2) never bound radiolabeled CK isoenzymes, and was not adsorbed to Protein A. Electrophoretic migration of this macro-CK type 2 was generally cathodic to CK-MM. We observed this type in severely ill patients, frequently those suffering from malignant tumors. Clinical observations and biochemical data suggest that macro-CK type 2 is of mitochondrial origin.