On the fate of glycogen phosphorylase in the ischemic and infarcting myocardium

Abstract

It is believed that glycogen phosphorylase and other enzymes of the glycogen cycle exist in the cell in a macromolecular complex with glycogen. When the glycogen stores become depleted, this complex is disrupted and conditions are created that facilitate the destruction and loss of phosphorylase. Experiments are reviewed which provide evidence that during incubation of 10 μm sections of ischemic, glycogen-depleted heart muscle the phosphorylase easily diffuses out into the medium. This is apparently the reason why histochemists have been led to believe that phosphorylase disappears within a few minutes in ischemic myocardium, although the loss of the enzyme from intact, i.e. not sectioned, ischemic and infarcting heart muscle can be demonstrated by quantitative biochemical analyses to be a slow process that goes on for many hours. Phosphorylase has been found, along with other enzymes, to appear or rise in the blood serum of animals following temporary ligation of a limb. The enzyme is also released from the isolated perfused heart following a temporary interruption of perfusion. If a method for determining phosphorylase can be developed that is sufficiently sensitive to permit the detection and measurement of the enzyme in the serum of patients, the existence of a heart-specific isoenzyme of phosphorylase could be made use of in the differential diagnosis of myocardial infarction.