Abstract

Methods are described (a) for the estimation of glycogen phosphorylase activity (EC 2.4.1.1) in human blood serum based on the chemical determination of liberated orthophosphate or on the enzymic determination of glucose 1-phosphate in a coupled assay system and (b) for the electrophoretic separation of isophosphorylases I, II, and III in human. Glycogen phosphorylase activities ranging from 1.5 to 18 mU/ml were found in the serum of patients with acute myocardial infarction. In contrast, no glycogen phosphorylase activity was detected in the serum of healthy persons. The enzyme appears in the serum 4 hours after the onset of the infarction and reaches a maximum after 20 to 30 hours. Acrylamide gel electrophoresis of serum after a myocardial infarction revealed only muscle isophosphorylase I, the isoenzyme characteristic of the heart. No phosphorylase activity was detected in serum of patients with angina pectoris, endocarditis, and uncomplicative congestive heart failure. From these findings it appears that the new serum enzyme test may prove to be a valuable addition to presently existing methods for the early differential diagnosis of acute myocardial infarction.