Enzymological investigations on the causes for the PSE-syndrome, II. Comparative studies on glycogen phosphorylase from pig muscles

• Published in: Meat science 1996-09, Vol.44 (1), p.41-53
• Main Authors: Schwägele, F., Buesa, P.L.Lopez, Honikel, K.O.
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Food industries; Fundamental and applied biological sciences. Psychology; Meat and meat product industries
• ISSN: 0309-1740; 1873-4138
• DOI: 10.1016/S0309-1740(96)00045-9

In order to investigate the cell biological causes for the fast breakdown of glycogen which is observed during the development of the PSE (pale, soft, exudative) syndrome in muscles of stress-susceptible pigs, muscle glycogen phosphorylase (GP) as a key enzyme in two isoforms, a and b, of the energy turnover was isolated from M. longissimus dorsi of normal and PSE-prone pigs of the German Landrace. GP b as well as GP a from normal and PSE-muscles exist in a dimeric form with a molecular weight of 97 000 D per subunit. The tendency for tetramerization of GP b increases in the presence of ATP, whereas the enzyme activity is simultaneously inhibited. The catalytic activities of GP a and GP b from both groups of animals show an optimum at pH 7.0. GP b can be activated to GP a by phosphorylation with the result of a 25% higher optimum specific activity in the case of normal and PSE-muscles. In interaction with glycogen and glucose-1-phosphate GP b follows the characteristics of a Michaelis-Menten kinetic, whereas the binding of AMP and phosphate proves to be allosteric. In comparison of the structural and kinetic characteristics of GP from normal as well as PSE-muscles no significant differences could be determined, indicating that GP does not belong to those factors which are triggering an accelerated energy turnover of ATP in muscles of stress-susceptible pigs.