Electrophoretic Characteristics of Macro Creatine Kinase Type

We have studied the electrophoretic characteristics of a creatine kinase (CK, EC 2.7.3.2) isoenzyme, macro creatine kinase type 2 (MCK-2), in the serum of 42 patients wIth carcinoma of the colon. The patients could be divided into three subgroups by the intensity of the MCK-2 band (nine high, nine medium, and 24 low intensity), but we detected no correlation between the isoenzyme activity and the stage of the cancer. Inhibition of the activity of the CK-M subunit by antibody to CK-M allowed more sensitive detection of MCK-2 in serum and revealed that MCK-2 may be obscured by CK-MM. Moreover, there may be major discrepancies between the amount of MCK-2 seen on electrophoresis and the apparent total CK. AddItional Keyphrasee: isoenzymes carcinoma of the colon immunoinhibition electrophoresis, agarose cancer The isoenzyme of creatine kinase (CK, EC 2.7.3.2) that migrates cathodally to CK-MM on agarose gel electrophore-sin is of special interest to clinical biochemists, having been investigated as a potential serum marker for cancer (1-9) and for myocardial damage (10-12). Its presence in serum may indicate a poor prognosis (13-15). It has a high molecular mass, does not contain immunoglobulin, and has been variously called CK,mt and macro CK type 2 (MCK-2) (6, 15-17). Elsewhere, we have described its utility as a tumor marker in patients with carcinoma of the colon (18) and have detailed its purification from tumor tissue, from normal colonic mucosa, and from carcinoma cells in tissue culture (19). Here we describe the various patterns seen on isoenzyme electrophoresis of serum from patients with carcinoma of the colon, and we discuss ways to increase the sensitivity with which the isoenzyme can be detected