Abstract
Three serum creatine phosphokinase (CPK) isoenzymes (MM, MB and BB) have been recognized. Myocardium is richly endowed with MB CPK. Accordingly, increased serum MB CPK activity reflects myocardial injury. Although recent advances have facilitated detection of activity of CPK isoenzymes, available techniques have unavoidable quantitative limitations. Accordingly, we used a new procedure to quantify CPK isoenzymes in serum samples with normal or increased total CPK activity. Samples were diluted or concentrated so that total CPK activity was 0.100 to 1.200 IU/ml and then subjected to electrophoresis on cellulose acetate. Regions of the strips encompassing each isoenzyme were cut out, immersed in 0.5 to 3 ml of assay medium in which the reduced form of nicotinamide adenine dinucleotide phosphate (NADPH) was generated as a function of isoenzyme activity. NADPH was detected by serial determinations of fluorescence in the medium. The assay was linear with respect to time and isoenzyme activity (0.010 to 1.2 ID/ml, no. = 100) and recovery averaged 83 ± 1.8 percent (standard deviation). Reproducibility was within 2 percent. Accuracy of the method was validated with selected mixtures of BB and MM isoenzymes. Serum MB CPK activity averaged only 0.002 ± 0.001 lU/ml in normal persons (no. = 27), compared to 0.064 ± 0.043 lU/ml in 30 patients with myocardial infarction. Serum MB CPK activity was not increased in 23 patients after intramuscular injections or abdominal surgery. The procedure described permits quantitative determination of activity of individual CPK isoenzymes in serum samples with or without increased total CPK activity and thus is of potential value in the quantitative assessment of myocardial infarction by serum enzyme analysis. © 1974.