Plasma Lysosomal Enzyme Activity in Acute Myocardial Infarction

N-acetyl-beta-glucosaminidase (EC 3.2.1.30, recommended name beta-N-Acetylglucosaminidase) was found to be a constituent of human cardiac lysosomes. beta-glucuronidase was also found in this tissue, while lysozyme, an enzyme present in leucocyte lysosomes, was not detectable in the heart. The activities of both N-acetyl-beta-glucosaminidase and beta-glucuronidase were elevated in plasma during the first 24 h after the onset of chest pain in patients with acute myocardial infarction and the peak levels of N-acetyl-beta-glucosaminidase correlated well with those of creatine kinase. N-acetyl-beta-glucosaminidase showed a further rise in plasma activity which gave a peak at 72 h after the onset of chest pain and this was accompanied by a rise in lysozyme activity. It is suggested that lysosome disruption caused by myocardial cell necrosis was responsible for the initial rise in plasma lysosomal enzyme activity and that the subsequent inflammatory reaction gave rise to the second peak.