Time dependent conversion of creatine kinase MM isoforms in man.

Subforms of creatine kinase MM isoenzyme (isoforms, pI: MMA = 7.95, MMB = 7.76, MMC = 7.54) in human myocardium and serum were quantified by chromatofocusing. Creatine kinase MMA was a dominant isoform (greater than 94% of MM) in normal (n = 3) and in both infarcted and non-infarcted myocardium (n = 2). To investigate isoform conversion in vitro partially purified MMA was incubated with human plasma at 37 degrees C for 24 h (n = 5). Creatine kinase MMB (0%, 47%, 44% of MM at 0, 12, 24 h respectively) and MMC (0%, 22%, 42%) sequentially appeared in incubation media whereas MMA (100%, 31%, 14%) disappeared rapidly with a mean disappearance rate of -0.00169(0.00021)(SD) min-1. Individual differences in conversion velocity were small (SD less than 5%). To investigate isoform conversion in vivo serum isoforms were analysed in patients with acute myocardial infarction (n = 7). MMA was first dominant (A:B:C = 54:34:12%) in the early stage (6-9 h after the onset of chest pain) followed by MMB dominant (19:42:39%) in the middle stage (24-35 h), and MMC dominant (6:22:72%) in the late stage (54-60 h). Changes in isoform proportion were time dependent regardless of serum creatine kinase activity. These findings are consistent with canine isoform conversion reported previously except that in man the velocity of conversion was slower than in the dog. Thus analysis of serum creatine kinase MM isoforms may allow the onset of acute myocardial infarction to be precisely dated. Moreover, determination of MMA, the isoform native to myocardium with a short serum half life, may be useful in the prompt diagnosis of myocardial infarction.