ACTIVITY OF PHOSPHOGLYCERATE MUTASE AND ITS ISOENZYMES IN SERUM AFTERACUTE MYOCARDIAL-INFARCTION

Aims/background-In humans there are three phosphoglycerate mutase (PGM , EC 5.4.12.1) isoenzymes (MM, MB and BE) which have similar distribut ion and developmental pathways to creatine kinase (CK, EC 2.7.3.2) iso enzymes. Total serum PGM activity increases in acute myocardial infarc tion with the same time course as creatine kinase activity. The presen t study was undertaken to determine changes in the activity of PGM and its isoenzymes after acute myocardial infarction. Methods-PGM activit y was measured spectrophotometrically, by coupling the formation of 2- phosphoglycerate from 3-phosphoglycerate with enolase, pyruvate kinase and lactate dehydrogenase catalysed reactions. Inter- and intra-assay reproducibility was assessed. PGM isoenzyme activities were measured using cellulose acetate electrophoresis. Results-Total PGM activity in serum was increased in patients with a confirmed diagnosis of acute m yocardial infarction. PGM activity peaked 12 to 24 hours after the ons et of symptoms and returned to normal values within 48 hours. Electrop horetic analysis of serum from healthy subjects showed a band correspo nding to BB-PGM and two other artefactual bands that did not correspon d to adenylate kinase. After myocardial infarction, BB-PGM activity in creased and MB-PGM and MM-PGM could be detected. On immunoblot analysi s, normal serum contained an inactive form of MM-PGM with a smaller mo lecular weight than that of PGM tissue isoenzymes. Conclusions-Total s erum PGM activity increased in patients with acute myocardial infarcti on, following the same temporal course as creatine kinase activity. Th e increase in MM-PGM and MB-PGM activities in these patients was not a s high as expected. It is suggested that PGM isoenzymes, after release into the blood, undergo postsynthetic, probably proteolytic, transfor mation.