Changes in solubility and enzymic activity of muscle glycogen phosphorylase in PSE-muscles

Comparison of the crude extracts of soluble proteins of PSE (pale, soft and exudative) and normal porcine muscles shows that the solubility and activity of muscle glycogen phosphorylase are diminished in PSE muscles. In the insoluble fractions of the muscle extract, however, an increased amount of a protein with the molecular weight of the phosphorylase subunit (92·500-95·000) can be found by means of SDS-electrophoresis. The PSE conditions with high temperatures of 36-40°C in the first hour post mortem and a low pH of 5·3-5·8 at the same time post mortem are simulated with normal porcine muscles at twenty-four hours post mortem which causes the same change in solubility and activity of muscle glycogen phosphorylase as in PSE muscles. This proves, for the first time, that low pH and high temperature in whole muscles cause a denaturation of phosphorylase, as indicated by both reduced activity and decreased solubility. Previous studies have looked only at one of these aspects. This supports the hypothesis of Bendall & Wismer-Pedersen (1962) that in PSE muscles a partial denaturation of sarcoplasmic protein occurs.