heterogeneity of creatine kinase isoenzyme MM in serum in myocardial infarction: interconversion of the "normal" and "abnormal" sub-bands by glutathione

We used isoelectric focusing (IEF) in polyacrylamide gels to investigate the effects of glutathione on the sub-bands of serum creatine kinase (CK; EC 2.7.3.2) isoenzyme MM in acute myocardial infarction. The intensity of the "abnormal" sub-bands c (pI 7.25), e (pI 6.85), and g (pI 6.50) increased, and that of the "normal" sub-bands 1 (pI 6.91), 2 (pI 6.65), and 3 (pI 6.35) decreased, following serum incubation with reduced glutathione (GSH, final concentration 1.25 mmol/L). Further incubation with oxidized glutathione (GSSG, final concentration 5 mmol/L) reversed this change and restored the original pattern, whereas GSSG at 7.5 mmol/L caused sub-bands c, e, and g to disappear and sub-bands 1, 2, and 3 to be enhanced. Sequential incubation of serum with 2.5 mmol of GSSG and 7.5 mmol of GSH per liter produced the opposite sequence of events; i.e., the "abnormal" sub-bands disappeared then reappeared (and GSH at 10 mmol/L enhanced their reappearance). At higher concentrations, glutathione (GSH or GSSG) impaired the detection of the CK-MM sub-bands after IEF, an effect that was "quenched" by heat-inactivated serum of low CK activity. Likewise, the intensity of tissue CK-MM (corresponding to myocardium extracted into 100 mmol/L Tris HCl buffer, pH 7.4) was greatly enhanced by adding heat-inactivated serum to the tissue extract before IEF. We discuss the significance of these findings for the diagnosis of myocardial infarction.