Abnormal electrophoretic mobility of creatine kinase isoenzyme in serum of an otherwise healthy person.

We describe the abnormal electrophoretic mobility of a creatine kinase isoenzyme in the serum of an apparently healthy individual. In agarose gel electrophoresis this isoenzyme migrates more toward the cathode than does the MM isoenzyme. It is more resistant to heat and more strongly inhibited by urea than the normal MM isoenzyme. We performed gel filtration, on a Sephadex G-200 column, of the patient's serum and observed two distinct isoenzymes with different relative molecular masses; a normal isoenzyme of 80,000 daltons and another abnormal one of 240,000 daltons. We performed serum immunoelectrophoresis but did not observe any immune complex formation involving the abnormal isoenzyme.